Lithium ion secondary battery and manufacturing method therefor

ABSTRACT

Active material particles of a lithium ion secondary battery includes at least a first lithium-nickel composite oxide: Li x Ni 1-y-z Co y Me z O 2  (where 0.85≦x≦1.25, 0&lt;y≦0.5, 0≦z≦0.5, 0&lt;y+z≦0.75, and element Me is at least one selected from the group consisting of Al, Mn, Ti, Mg, and Ca) forming a core portion thereof. The surface layer portion of the active material particles includes nickel oxide having the NaCl-type crystal structure or a second lithium-nickel composite oxide, and further includes element M not forming the crystal structure of the first lithium-nickel composite oxide. Element M is at least one selected from the group consisting of Al, Mn, Mg, B, Zr, W, Nb, Ta, In, Mo, and Sn.

RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT/JP2006/305730, filed on Mar. 22, 2006, which in turn claims the benefit of Japanese Application No. 2005-084445, filed on Mar. 23, 2005, the disclosures of which Applications are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a lithium ion secondary battery that is excellent in safety at the time of an internal short-circuit.

BACKGROUND ART

Lithium ion secondary batteries, a typical example of non-aqueous electrolyte secondary batteries, have high electromotive force and high energy density. Thus, demand is growing for lithium ion secondary batteries, as a main power source for mobile telecommunication devices and mobile electronic devices. A majority of lithium ion secondary batteries currently on the market include a lithium composite oxide containing cobalt as its main component (for example, Li_(x)CoO₂ (x changes based on charging and discharging of the battery)) as the positive electrode active material. However, cost reduction is difficult because of the high price of cobalt compound used as the raw material in lithium composite oxide containing cobalt as a main component.

Therefore, in view of cost reduction, there have been researches and developments for an alternative to lithium composite oxide containing cobalt as a main component. Particularly, active researches have been carried out for lithium composite oxide containing nickel as a main component (for example, Li_(x)NiO₂ (x changes based on charging and discharging of the battery)).

In addition to cost reduction, it is important to increase reliability of lithium ion secondary batteries. The lithium composite oxide including Co or Ni produces high valence, highly reactive Co⁴⁺ or Ni⁴⁺ upon charging. This accelerates electrolyte decomposition reaction involving lithium composite oxide under high temperature environment. As a result, gas generation occurs, and it becomes difficult to curb heat generation at the time of an internal short-circuit.

In charged batteries, Li_(x)NiO₂ is more reactive than Li_(x)CoO₂. Thus, curbing of the electrolyte decomposition reaction has been examined. For example, there has been proposed that nickel oxide with the nickel oxidation number of 3 or less and not including lithium in its crystal is added to the lithium composite oxide containing nickel as its main component (Patent Document 1). Additionally, there has been proposed that a coating comprising a specific metal oxide is formed on the positive electrode active material surface (Patent Documents 2 to 5). Further, there have been proposed that the positive electrode active material surface is reduced (Patent Document 6). For example, there has been proposed that the positive electrode active material surface is reduced with gas and the positive electrode active material is mixed with carbon and then baked.

Patent Document 1:

Japanese Laid-Open Patent Publication No. Hei 7-134985

Patent Document 2:

Japanese Laid-Open Patent Publication No. Hei 8-236114

Patent Document 3:

Japanese Laid-Open Patent Publication No. 2003-123750

Patent Document 4:

Japanese Laid-Open Patent Publication No. Hei 11-16566

Patent Document 5:

Japanese Laid-Open Patent Publication No. 2001-256979

Patent Document 6:

Japanese Laid-Open Patent Publication No. Hei 10-199530

DISCLOSURE OF INVENTION Problem that the Invention is to Solve

As mentioned above, there have been many proposals for curbing gas generation. However, for securing battery reliability sufficiently, the reaction involving lithium composite oxide has to be curbed to a further high degree. To be specific, prevention of battery abnormal heat generation upon internal short-circuit is desired. For example, it is desired to curb battery abnormal heat generation at the time of crush test under environment of 60° C. In view of this, there is still room for improvement in techniques in Patent Documents 1 to 6.

Reasons for the occurrence of abnormal heat generation in battery at the time of an internal short-circuit is described here.

When an internal short-circuit occurs, Joule heat is generated at the short circuit portion. That heat induces thermal decomposition reaction of the positive electrode active material and reactions between the active material and the electrolyte. These reactions involve heat generation. Therefore, when these reactions cannot be curbed, it leads to abnormal heat generation in a battery.

Thermal decomposition reaction of the active material is oxygen desorption reaction from the active material surface. Electrolyte decomposition reaction is a reaction between the active material surface and the electrolyte. As a result of various examinations, there have been obtained findings that these reactions advance at active points of the active material surface. The active point of the active material surface is formed by lattice defect.

According to Patent Document 1, a nickel oxide with nickel oxidation number of three or less and not including lithium in its crystal works to curb electrolyte decomposition reactions. However, merely adding the nickel oxide to the active material leaves the active point on the active material surface existed. Thus, when the crush test is carried out under a harsh environment of 60° C., there is a possibility that battery abnormal heat generation is caused.

According to Patent Documents 2 to 5, a metal oxide film formed on the active material surface can curb the reaction between the active material surface and the electrolyte. However, the active point on the active material surface is not completely inert. Thus, oxygen desorption of the active material cannot be curbed.

According to Patent Document 6, by reducing the whole active material surface, reactivity of the whole surface declines. Thus, thermal decomposition reaction of the positive electrode active material and reaction between the active material and the electrolyte can be curbed. However, a problem occurs in which high-rate performance cannot be obtained sufficiently at low temperature.

Means for Solving the Problem

The present invention aims to further improve safety at the time of an internal short-circuit in a lithium ion secondary battery including a lithium composite oxide (lithium-nickel composite oxide) which contains nickel as its main component and has a crystal structure of for example R3-m as the positive electrode active material, without hindering high-rate performance at low temperature.

That is, the present invention relates to a lithium ion secondary battery comprising a positive electrode capable of charging and discharging, a negative electrode capable of charging and discharging, and a non-aqueous electrolyte;

the positive electrode including active material particles;

the active material particles including at least a first lithium-nickel composite oxide forming a core portion thereof;

the first lithium-nickel composite oxide being represented by Li_(x)Ni_(1-y-z)Co_(y)Me_(x)O₂

where 0.85≦x≦1.25, 0<y≦0.5, 0≦z≦0.5, 0<y+z≦0.75, and element Me is at least one selected from the group consisting of Al, Mn, Ti, Mg, and Ca;

a surface layer portion of the active material particles including:

(i) at least one selected from the group consisting of a nickel oxide having a NaCl-type crystal structure and a second lithium-nickel composite oxide including a domain having the NaCl-type crystal structure; and

(ii) element M not incorporated in the crystal structure of the first lithium-nickel composite oxide, element M being at least one selected from the group consisting of Al, Mn, Mg, B, Zr, W, Nb, Ta, In, Mo, and Sn.

The nickel oxide having the NaCl-type crystal structure is preferably at least one selected from the group consisting of NiO and cation-deficient Ni_(1-δ)O. Also, the domain having the NaCl-type crystal structure is preferably structured so that Li in Li site in the first lithium-nickel composite oxide is replaced with Ni, Co, or Me.

In one embodiment of the present invention, element M is distributed more in the outer side of the surface layer portion than in the inner side, and nickel oxide is distributed more in the inner side of the surface layer portion than in the outer side.

In one embodiment of the present invention, the above general formula satisfies 0<z≦0.5, and the concentration of element Me is higher in the proximity of the surface layer portion of the active material particles compared with the inner side thereof.

The amount of element M is preferably 2 mol % or less relative to the lithium-nickel composite oxide.

The present invention also relates to a method for producing a lithium ion secondary battery, the method comprising the steps of:

obtaining a positive electrode capable of charging and discharging;

obtaining a negative electrode capable of charging and discharging; and

assembling a battery including the positive electrode, the negative electrode, and a non-aqueous electrolyte:

the step of obtaining the positive electrode including:

(i) allowing a first lithium-nickel composite oxide represented by Li_(x)Ni_(1-y-z)Co_(y)Me_(z)O₂

where 0.85≦x≦1.25, 0<y≦0.5, 0≦z≦0.5, 0<y+z≦0.75, and element Me is at least one selected from the group consisting of Al, Mn, Ti, Mg, and Ca to carry at least one element M selected from the group consisting of Al, Mn, Mg, B, Zr, W, Nb, Ta, In, Mo, and Sn;

(ii) producing NiOOH on the surface of the first lithium-nickel composite oxide by moisture in the atmosphere by allowing the first lithium-nickel composite oxide carrying element M to stand under an environment with a temperature of 60° C. or less and a humidity of 20% or more;

(iii) preliminary baking the first lithium-nickel composite oxide with NiOOH produced on the surface thereof in a dry air atmosphere, and then carrying out a main baking in an oxygen atmosphere, thereby converting NiOOH into at least one selected from the group consisting of NiO having a NaCl-type crystal structure, cation-deficient Ni_(1-δ)O having the NaCl-type crystal structure, and a second lithium-nickel composite oxide including a domain having the NaCl-type crystal structure, to obtain active material particles; and

(iv) forming a positive electrode including the active material particles.

EFFECTS OF THE INVENTION

Based on the present invention, safety at the time of an internal short-circuit can be improved than before in a lithium ion secondary battery including a lithium composite oxide containing nickel as its main component (a first lithium-nickel composite oxide) as the positive electrode active material, without obstructing high-rate performance at low temperature.

The reasons that a high degree of safety can be secured at the time of an internal short-circuit have been only confirmed phenomenologically at this point. By adding element M to the surface of the first lithium-nickel composite oxide and exposing it to an environment satisfying predetermined conditions, only the active point of side reaction is converted into a second lithium-nickel composite oxide including NiO having the electrochemically inactive NaCl-type crystal structure, cation-deficient Ni_(1-δ)O having the NaCl-type crystal structure, or a domain having the NaCl-type crystal structure. The side reaction includes oxygen desorption reaction of the first lithium-nickel composite oxide and electrolyte decomposition reaction. Since only the side reaction active point of the surface layer portion of the active material particles is converted into electrochemically inactive oxide, decline in high-rate performance at low temperature is curbed.

It is difficult at this point to clearly analyze in what form element M (at least one selected from the group consisting of Al, Mn, Mg, B, Zr, W, Nb, Ta, In, Mo, and Sn) is contained at the surface layer portion of the active material particles. However, it is possible to distinguish, for example, Al, Mn, or Mg present at the surface layer portion, from Al, Mn, or Mg included in the crystal of the first lithium-nickel composite oxide by analysis such as electron diffraction measurement and EXAFS. In analysis, these can be distinguished by its crystal structure. The presence of element M at the surface layer portion of the active material particles can also be confirmed by analysis method such as element mapping by EPMA (Electron Probe Micro-Analysis).

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] A schematic cross sectional view of an example of an active material particle of the present invention.

[FIG. 2] A vertical cross section of a cylindrical lithium ion secondary battery of Example of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A positive electrode of the present invention is described first. The positive electrode includes active material particles as described below.

The active material particles include a first lithium-nickel composite oxide. The first lithium-nickel composite oxide may be in any form without limitation. The first lithium-nickel composite oxide may form active material particles, for example, with its primary particles and with secondary particles. The average particle size of the active material particles is preferably 1 to 30 μm, for example, without any limitation.

The first lithium-nickel composite oxide is represented by the general formula: Li_(x)Ni_(1-y-z)Co_(y)Me_(z)O₂ where 0.85≦x≦1.25, 0<y≦0.5, 0≦z≦0.5, 0<y+z≦0.75, and element Me is at least one selected from the group consisting of Al, Mn, Ti, Mg, and Ca. The first lithium-nickel composite oxide may include, as element Me, any of Al, Mn, Ti, Mg, and Ca, singly or in combination of two or more.

The value of x increases and decreases within the above range by battery charging and discharging. Co is an essential component, which gives an effect of decreasing the irreversible capacity to the first lithium-nickel composite oxide. Element Me is an arbitrary component which gives an effect of improving thermal stability to the first lithium-nickel composite oxide. When y or z exceeds 0.5, sufficient capacity cannot be obtained. Also, when y+z exceeds 0.75, the amount of Ni becomes below 0.25. Thus, it becomes difficult to produce NiOOH, NiO, Ni_(1-δ)O, or a second lithium-nickel composite oxide including a domain having the NaCl-type crystal structure.

In view of achieving both battery performance and safety, the ranges of y and z are preferably 0.05≦y≦0.25 and 0.001≦z≦0.1, respectively, and further preferably 0.08≦y≦0.2 and 0.005≦z≦0.05, respectively.

The first lithium-nickel composite oxide is synthesized by baking a raw material having a predetermined metal element ratio in an oxidizing atmosphere. The raw material includes lithium, nickel, cobalt, and element Me, i.e., an arbitrary component. The raw material includes oxides, hydroxides, oxyhydroxides, carbonates, nitrates, and organic complex salts of each metal element. These may be used singly, or may be used in combination of two or more.

In view of making the synthesizing of the first lithium-nickel composite oxide easy, the raw material preferably includes a solid solution containing a plurality of metal elements. The solid solution including a plurality of metal elements may be oxides, hydroxides, oxyhydroxides, carbonates, nitrates, and organic complex salts. For example, a solid solution including Ni and Co, a solid solution including Ni and element Me, a solid solution including Co and element Me, and a solid solution including Ni, Co, and element Me are preferably used.

Baking temperature and oxygen partial pressure of the oxidizing atmosphere for the raw material depend on the composition, amount, and synthesizing device of the raw material. Those skilled in the art can select appropriate conditions as appropriate.

An element other than Li, Ni, Co, and element Me is sometimes mixed in as impurities in a range of amount usually included in industrial raw materials. However, the impurities may not affect the present invention greatly.

The surface layer portion of the active material particles includes at least one selected from the group consisting of nickel oxide having the NaCl-type crystal structure and a second lithium composite oxide including a domain having the NaCl-type crystal structure. Nickel oxide having the NaCl-type crystal structure is preferably at least one selected from the group consisting of NiO and cation-deficient Ni_(1-δ)O. The surface layer portion may include any one of NiO, cation-deficient Ni_(1-δ)O, and a second lithium-nickel composite oxide, singly or in combination of two or more.

Presence of NiO and cation-deficient Ni_(1-δ)O may be confirmed by X-ray diffraction measurement (XRD) and XENES measurement. The second lithium-nickel composite oxide including the domain having the NaCl-type crystal structure may be confirmed by electron diffraction measurement.

δ preferably satisfies 0≦δ≦0.1. In the following, nickel oxide of at least one selected from the group consisting of NiO and cation-deficient Ni_(1-δ)O is also called Ni_(1-δ)O (0≦δ).

When the amount of Ni_(1-δ)O(0≦δ) or the domain having the NaCl-type crystal structure is excessively small to the extent that its presence cannot be confirmed, sometimes the effects of curbing oxygen desorption reaction of the first lithium-nickel composite oxide and reaction between the first lithium composite oxide and electrolyte become insufficient.

The surface layer portion of the active material particles further includes at least one element M selected from the group consisting of Al, Mn, Mg, B, Zr, W, Nb, Ta, In, Mo, and Sn. The surface layer portion may include the above element singly as element M, or a plurality of the above elements may be combined arbitrary. Element M contributes to deactivation of side reaction active point of the first lithium-nickel composite oxide. Element M is preferably present at the surface layer portion of the active material particles as oxides. Also, element M is preferably deposited, attached, or carried at the first lithium-nickel composite oxide surface as oxides.

Sometimes the surface layer portion of the active material particles include at least one selected from the group consisting of Al, Mn, and Mg as element M, and the lithium composite oxide includes at least one selected from the group consisting of Al, Mn, and Mg as element Me. In this case, Al, Mn, and Mg as element M contributing to deactivation of side reaction active point of the lithium composite oxide is different from Al, Mn, and Mg as element Me forming lithium composite oxide in the crystal structure. Therefore, these can be clearly distinguished.

However, there may be a case where Al, Mn, and Mg at the surface layer portion diffuse into the first lithium-nickel composite oxide inside the active material particles. That is, there may be a case in which element M at the surface layer portion changes into element Me forming the first lithium-nickel composite oxide. In this case, an Al, Mn, or Mg concentration in the first lithium-nickel composite oxide becomes high in the proximity of the surface layer portion compared with the inner portion of the active material particles.

FIG. 1 is a schematic cross sectional view of an example of an active material particle 10.

The active material particle 10 includes at least a first lithium-nickel composite oxide 11 forming a core portion thereof, and a surface layer portion 12 existing at a surface of the first lithium-nickel composite oxide 11. An oxide of element M 13 is attached to a surface of the first lithium-nickel composite oxide 11. Nickel oxide having the NaCl-type crystal structure or a second lithium-nickel composite oxide 14 is formed mainly at an inner side of the oxide of element M 13. That is, the oxide of element M 13 mainly forms the outer side of the surface layer portion 12, and nickel oxide or the second lithium-nickel composite oxide 14 mainly forms the inner side of the surface layer portion 12.

The first lithium-nickel composite oxide 11 forming the core portion of the active material particle 10 may be primary particles, or may be secondary particles formed by the aggregation of a plurality of the primary particles. Also, a plurality of the active material particles 10 may be aggregated to form the secondary particles.

For the raw material for element M included in the surface layer portion of the active material particles, sulfates, nitrates, carbonates, chlorides, hydroxides, oxides, and alkoxides are preferably used. These may be used singly, or may be used in combination of two or more. Among these, sulfates, nitrates, chlorides, or alkoxides are preferably used particularly, since Ni_(1-δ)O (0≦δ) and the second lithium-nickel composite oxide are easily produced at the surface layer portion.

The amount of element M included in the active material particles is preferably 2 mol % or less relative to the first lithium-nickel composite oxide (when x=1, Li in the first lithium-nickel composite oxide). When the amount of element M exceeds 2.0 mol %, there may be a case where the active material surface is excessively covered with the oxide not contributing to reactions, declining high-rate performance at low temperature. Element M may be used in small amount, but preferably element M is 0.01 mol % or more, and further preferably 0.1 mol % or more relative to the first lithium-nickel composite oxide.

An example of a method of manufacturing a positive electrode is described next. First, a case in which Ni_(1-δ)O (0≦δ) is produced at the surface layer portion of the active material particles is described. In this case, side reaction active point of the first lithium-nickel composite oxide involved with oxygen desorption and electrolyte decomposition is converted to Ni_(1-δ)O (0≦δ).

(i) First Step

First, element M of at least one selected from the group consisting of Al, Mn, Mg, B, Zr, W, Nb, Ta, In, Mo, and Sn is carried on a first lithium-nickel composite oxide represented by the general formula Li_(x)Ni_(1-y-z)Co_(y)Me_(z)O₂(x≦1.02). The average particle size of the first lithium-nickel composite oxide is not particularly limited, but preferably, for example, 1 to 30 μm.

The method for allowing the first lithium-nickel composite oxide to carry element M is not particularly limited. For example, a raw material for element M is dissolved or dispersed in a liquid component, to prepare a solution or a dispersion. For the raw material of element M, sulfates, nitrates, carbonates, chlorides, hydroxides, oxides, and alkoxides including element M are used. The obtained solution or dispersion is mixed with the first lithium-nickel composite oxide, and afterwards, the liquid component is removed.

The liquid component for dissolving or dispersing the raw material of element M is preferably an organic solvent, though not particularly limited. For example, ketones such as acetone and methylethylketone (MEK), ethers such as tetrahydrofuran (THF), and alcohols such as ethanol are preferable. An alkaline water of pH 10 to 14 is also preferably used.

After introducing the first lithium-nickel composite oxide to the obtained solution or dispersion, the mixed solution is stirred. At that time, the temperature in the liquid is preferably set to for example 80 to 150° C., to easily advance the reaction. Although the stirring time is not particularly limited, for example, 3 hours is sufficient. The method for removing the liquid component is not particularly limited, but the drying is carried out for example at a temperature of about 100° C. for 2 hours.

(ii) Second Step

Next, the first lithium-nickel composite oxide carrying element M is allowed to stand under an environment with a temperature of 60° C. or less and a humidity of 20% or more, preferably for 2 to 48 hours. For example, the first lithium-nickel composite oxide carrying element M is allowed to stand under an environment with a temperature of about 25° C. and a humidity of about 55% for about 24 hours. During this time, NiOOH is produced by moisture in the atmosphere at the surface of the first lithium-nickel composite oxide. At that time, moisture is chemisorped to the side reaction active points at the first lithium-nickel composite oxide surface on a priority basis. Therefore, the side reaction active points can be converted to NiOOH on a priority basis.

There is a possibility that portions other than the side reaction active points are also converted to NiOOH when the humidity is excessively high, or the temperature is high, i.e., exceeding 60° C., in the environment where the first lithium-nickel composite oxide carrying element M is allowed to stand. Allowing to stand for an excessively long period of time also causes the same result. In this case, sufficient charge and discharge capacity may not be secured. Preferable temperature for the environment for allowing the first lithium-nickel composite oxide carrying element M to stand is 10 to 55° C., and preferable humidity is 25 to 60%.

(iii) Third Step

The first lithium-nickel composite oxide with NiOOH produced on the surface thereof is preliminary baked in dry air, and then baked in an oxygen atmosphere. By such baking, NiOOH is converted to Ni_(1-δ)O (0≦δ). The baking conditions are not particularly limited, as long as NiOOH is reduced to Ni_(1-δ)O (0≦δ) under such conditions. The produced Ni_(1-δ)O (0≦δ) forms the surface layer portion of the active material particles along with element M. Element M is usually converted to oxide by baking. Ni_(1-δ)O (0≦δ) is made by partially converting nickel of the first lithium-nickel composite oxide. Therefore, Ni_(1-δ)O (0≦δ) is distributed to the inner side of the surface layer portion, and oxide of element M is distributed to the outer side.

When element M is not present at the first lithium-nickel composite oxide surface, upon converting NiOOH to Ni_(1-δ)O (0≦δ), portions other than the side reaction active points are also deactivated. Therefore, the active material particles with sufficient capacity cannot be obtained. That is, element M works to stabilize the first lithium-nickel composite oxide, and to curb a modification thereof. Upon converting NiOOH to Ni_(1-δ)O (0≦δ), water is thought to be released. Element M is thought to curb deterioration of the first lithium-nickel composite oxide by the released water.

An example of baking conditions is described in the following.

Baking of the first lithium-nickel composite oxide with NiOOH produced on the surface thereof is preferably carried out by the following three steps, in view of reliably converting the side reaction active points to Ni_(1-δ)O (0≦δ).

First, the first lithium-nickel composite oxide with NiOOH produced on the surface thereof is baked at 300 to 450° C. for about 2 to 24 hours (preferably for 6 hours) in a dry air atmosphere. At this time, the humidity of the dry air atmosphere is preferably 2 to 19%, and the pressure is preferably 101 to 50 KPa.

Then, the baking is carried out at 650 to 750° C. for 2 to 24 hours (preferably for 6 hours) under an oxygen atmosphere. At this time, the pressure of the oxygen atmosphere is preferably 101 to 50 KPa. Afterwards, annealing is further carried out at a temperature of 300 to 500° C., preferably at about 400° C. under an oxygen atmosphere. At this time, the pressure in the oxygen atmosphere is preferably 101 to 50 KPa. The oxygen atmosphere may include components other than oxygen, for example, moisture. However, the oxygen partial pressure is preferably 20% or more (when the pressure in the oxygen atmosphere is set as P and the oxygen partial pressure is set as Po, 0.2≦Po/P≦1).

(iv) Fourth Step

A positive electrode is formed by using the active material particles. The method for making the positive electrode is not particularly limited. Generally, the positive electrode is made by allowing a strip-like positive electrode core material (positive electrode current collector) to carry a positive electrode material mixture including active material particles and a binder. To the positive electrode material mixture, an additive such as a conductive material may also be included as an arbitrary component. A paste is prepared by dispersing the positive electrode material mixture in a liquid component, and the paste is applied on the core material and dried, to allow the core material to carry the positive electrode material mixture.

Described next is a case where a second lithium-nickel composite oxide including a domain having the NaCl-type crystal structure is produced on the surface layer portion of the active material particles.

(i) First Step

A first lithium-nickel composite oxide is allowed to carry element M by carrying out operations in the same manner as the case where the side reaction active points are converted to Ni_(1-δ)O (0≦δ), except that the first lithium-nickel composite oxide represented by the general formula Li_(x)Ni_(1-y-z)Co_(y)Me_(x)O₂ (1.03≦x) is used.

(ii) Second Step

Operations are carried out in the same manner as the case where the side reaction active points are converted to Ni_(1-δ)O (0≦δ), to convert the side reaction active points of the first lithium-nickel composite oxide to NiOOH.

(iii) Third Step

The first lithium-nickel composite oxide with NiOOH produced on the surface thereof is baked. By this baking, NiOOH reacts with surplus Li in the first lithium-nickel composite oxide. At that time, a second lithium-nickel composite oxide including a domain having the NaCl-type crystal structure is produced.

The baking conditions are not particularly limited, as long as NiOOH and surplus Li are reacted under such conditions. The produced second lithium-nickel composite oxide forms the surface layer portion of the active material particles along with element M. Element M is usually converted to oxide by baking. The second lithium-nickel composite oxide is made by partially converting the first lithium-nickel composite oxide. Therefore, the second lithium-nickel composite oxide is distributed to the inner side of the surface layer portion, and oxide of element M is distributed to the outer side.

Similarly to the case where the side reaction active points are converted to Ni_(1-δ)O (0≦δ), when element M is not present at the first lithium-nickel composite oxide surface, upon converting NiOOH to the second lithium-nickel composite oxide, portions other than the side reaction active points are also modified to the second lithium-nickel composite oxide. Therefore, the active material particles with sufficient capacity cannot be obtained.

An example of baking conditions is described in the following.

The first lithium-nickel composite oxide with NiOOH produced on the surface thereof is baked for 2 to 24 hours (preferably for 6 hours) at 400 to 750° C. under an oxygen atmosphere. At this time, the pressure of the oxygen atmosphere is preferably 101 to 50 KPa. The oxygen atmosphere may include components other than oxygen, for example, moisture. However, the oxygen partial pressure is preferably set to 20% or more (when the pressure of the oxygen atmosphere is set to P, and the oxygen partial pressure is set to Po, 0.2≦Po/P≦1).

(iv) Fourth Step

A positive electrode is made by carrying out operations in the same manner as the case where the side reaction active points are converted to Ni_(1-δ)O (0≦δ).

Elements such as Mg, Ti, Nb, and Ca are generally known to improve battery performance, reliability, and safety. Therefore, elements such as Mg, Ti, Nb, and Ca are preferably incorporated into the first lithium-nickel composite oxide to form a solid solution.

For the binder to be included in the positive electrode material mixture, a thermoplastic resin is preferable, although any of the thermoplastic resin and a thermosetting resin may be used. For the thermoplastic resin that can be used as the binder, for example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrenebutadiene rubber, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinylether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl acrylate copolymer, and ethylene-methyl methacrylate copolymer may be mentioned. These may be used singly, or may be used in combination of two or more. These may be crosslinked by ions of, for example, Na.

Any conductive material may be included in the positive electrode material mixture, as long as the material is an electron conductive material that is chemically stable in the battery. For example, graphites such as natural graphite (flake graphite) and artificial graphite; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powder such as aluminum powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxide such as titanium oxide; an organic conductive material such as polyphenylene derivative; and carbon fluoride may be used. These may be used singly, or may be used in combination of two or more. The amount of the conductive material to be added is not particularly limited, but preferably is 1 to 50 wt %, further preferably 1 to 30 wt %, and still further preferably 2 to 15 wt % relative to the active material particles included in the positive electrode material mixture.

The positive electrode core material (positive electrode current collector) may be any electron conductor, as long as it is chemically stable in the battery. For example, a foil or a sheet of aluminum, stainless steel, nickel, titanium, carbon, and conductive resin may be used. Particularly, aluminum foil and aluminum alloy foil are preferable. On the surface of the foil or the sheet, a layer of carbon or titanium may be added, and an oxide layer may be formed. Also, on the surface of the foil or sheet, unevenness may be added. For example, net, punched sheet, lath, porous material, formed material, fibrous molded material may be used. The thickness of the positive electrode core material is not particularly limited, but for example within a range of 1 to 500 μm.

In the following, elements other than the positive electrode are described. However, a lithium ion secondary battery of the present invention is characterized in that the positive electrode such as the above is included. Thus, elements other than the positive electrode are not particularly limited. The following is not to limit the present invention.

For the negative electrode capable of charging and discharging, for example, may be used is a negative electrode material mixture including a negative electrode active material and a binder, and including a conductive material and a thickener as arbitrary components being carried on a negative electrode core material. Such a negative electrode may be made by a method similar to that for the positive electrode.

The negative electrode active material may be a material capable of charging and discharging lithium electrochemically. For example, graphites, non-graphitizable carbon material, and lithium alloy may be used. The lithium alloy is preferably an alloy including particularly at least one selected from the group consisting of silicon, tin, aluminum, zinc, and magnesium. The average particle size of the negative electrode active material is not particularly limited, but preferably 1 to 30 μm.

The binder to be included in the negative electrode material mixture is not particularly limited, but for example, may be selected arbitrary from the materials shown as examples of the binder to be included in the positive electrode material mixture.

The conductive material to be included in the negative electrode material mixture may be any electron conductive material, as long as it is chemically stable in the battery. For example, graphites such as natural graphite (such as flake graphite) and artificial graphite; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as copper and nickel; and organic conductive material such as polyphenylene derivative may be used. These may be used singly, or may be used in combination of two or more. The amount of the conductive material to be added is not particularly limited, but preferably 1 to 30 wt %, and further preferably 1 to 10 wt % relative to the active material particles included in the negative electrode material mixture.

The negative electrode core material (negative electrode current collector) may be any electron conductor, as long as it is chemically stable in the battery. For example, a foil or sheet of stainless steel, nickel, copper, titanium, carbon, or conductive resin may be used. Copper foil or copper alloy foil is particularly preferable. On the surface of the foil or sheet, a layer of carbon, titanium, or nickel may be added, and an oxide layer may be formed. Also, on the surface of the foil or sheet, unevenness may be added. For example, net, punched sheet, lath, porous material, formed material, and fibrous molded material may be used. The thickness of the negative electrode core material is not particularly limited, but for example within a range of 1 to 500 μm.

For the non-aqueous electrolyte, a non-aqueous solvent dissolving a lithium salt therein is preferably used.

May be used for the non-aqueous solvent are, for example, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinylene carbonate (VC); chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), and dipropyl carbonate (DPC); aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate, and ethyl propionate; lactones such as γ-butyrolactone and γ-valerolactone; chain ethers such as 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), and ethoxymethoxyethane (EME); cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran; dimethylsulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethylmonoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethylether, 1,3-propanesultone, anisole, dimethylsulfoxide, and N-methyl-2-pyrrolidone. These may be used singly, but preferably used in combination of two or more. Particularly, a solvent mixture of cyclic carbonate and chain carbonate; or a solvent mixture of cyclic carbonate, chain carbonate, and aliphatic carboxylic acid ester is preferable.

The lithium salt to be dissolved in the non-aqueous solvent includes, for example, LiClO₄, LiBF₄, LiPF₆, LiAlCl₄, LiSbF₆, LiSCN, LiCl, LiCF₃SO₃, LiCF₃CO₂, Li(CF₃SO₂)₂, LiAsF₆, LiN(CF₃SO₂)₂, LiB₁₀Cl₁₀, lithium lower aliphatic carboxylate, LiCl, LiBr, LiI, LiBCl₄, lithium tetraphenylborate, and lithium imide salt. These may be used singly, or may be used in combination of two or more. However, at least LiPF₆ is used preferably.

The amount of lithium salt to be dissolved relative to the non-aqueous solvent is not particularly limited, but the lithium salt concentration is preferably 0.2 to 2 mol/L, and further preferably 0.5 to 1.5 mol/L.

Various additives may be added to the non-aqueous electrolyte for improving battery's charge and discharge performance. The additives include, for example, triethylphosphite, triethanol amine, cyclic ether, ethylenediamine, n-glyme, pyridine, hexaphosphoric triamide, nitrobenzene derivative, crown ether, quaternary ammonium salt, and ethylene glycol dialkylether.

A separator has to be interposed between the positive electrode and the negative electrode.

For the separator, a microporous thin film having a high ion permeability, a predetermined mechanical strength, and insulating ability is preferably used. The microporous thin film preferably has a function of closing the pores at a certain temperature or more, to increase the battery resistance. The material used for the microporous thin film preferably includes polyolefin (polypropylene and polyethylene) that is excellent in resistance to organic solvents and is hydrophobic. A sheet made of glass fiber, nonwoven fabric, and woven fabric are also used as the separator. The pore size of the separator is, for example, 0.01 to 1 μm. The thickness of the separator is generally 10 to 300 μm. The porosity of the separator is generally 30 to 80%.

A polymer electrolyte including a non-aqueous electrolyte and a polymer material retaining the electrolyte may be used instead of the separator. The polymer electrolyte may be integrated with the positive electrode or the negative electrode. The polymer material retaining the non-aqueous electrolyte is not particularly limited, but preferably, for example, a copolymer of vinylidene fluoride and hexafluoropropylene is preferable.

The present invention is described in detail based on Examples in the following, but the present invention is not limited to Examples below.

EXAMPLE 1 Example Battery A1 (i) Synthesis of First Lithium-nickel Composite Oxide

Nickel sulfate, cobalt sulfate, and aluminum sulfate were mixed so that a molar ratio of Ni atoms, Co atoms, and Al atoms was 80:15:5. The obtained mixture in an amount of 3.2 kg was dissolved in 10 L of water, to obtain a raw material solution. To the raw material solution, 400 g of sodium hydroxide was added to form a precipitate. The precipitate was sufficiently washed with water and dried, to obtain a coprecipitated hydroxide.

To 3 kg of the obtained coprecipitated hydroxide of Ni—Co—Al, 784 g of lithium hydroxide was mixed in, and the mixture was baked for 10 hours at a temperature of 750° C. under an atmosphere with an oxygen partial pressure of 0.5 atm, to obtain a first lithium-nickel composite oxide (LiNi_(0.8)Co_(0.15)Al_(0.05)O₂) including Al as element Me.

Various first lithium-nickel composite oxides were also synthesized by using various raw materials, instead of the above coprecipitated hydroxide of Ni—Co—Al. Evaluations were carried out for these as well, but the explanations are omitted in Examples below, since the obtained results were similar to the case of LiNi_(0.8)Co_(0.15)Al_(0.05)O₂.

(ii) Synthesis of Active Material Particles

<a> First Step

Tantalum pentaethoxide was dissolved in 10 L of ethanol. To the obtained solution, 2 kg of the synthesized first lithium-nickel composite oxide was dispersed. The amount of tantalum pentaethoxide dissolved in ethanol was set to 0.5 mol % relative to the first lithium-nickel composite oxide. The mixed solution of the first lithium-nickel composite oxide and the ethanol solution was stirred for 3 hours at 60° C. Afterwards, the mixed solution was filtrated and the residue thereof was dried for 2 hours at 100° C. As a result, a first lithium-nickel composite oxide carrying tantalum (Ta) as element M on the surface thereof was obtained.

<b> Second Step

The first lithium-nickel composite oxide (powder after drying) carrying tantalum on the surface thereof was allowed to stand under an environment with a temperature of 25° C. and a humidity of 55% for 24 hours. During this time, moisture in the atmosphere acted on the side reaction active points of the first lithium-nickel composite oxide surface to form NiOOH on the first lithium-nickel composite oxide surface. The formation of NiOOH was checked by XRD measurement and ESCA measurement.

<c> Third Step

The first lithium-nickel composite oxide with NiOOH formed on the surface thereof was baked preliminary for 6 hours at 300° C. under a dry air atmosphere (humidity 19%, pressure 101 KPa). Afterwards, a main baking was carried out for 6 hours at 650° C. under an atmosphere of 100% oxygen (pressure 101 KPa), and lastly, an annealing was carried out for 4 hours at 400° C. under an atmosphere of 100% oxygen (pressure 101 KPa). By this baking, NiOOH on the first lithium-nickel composite oxide surface is converted to Ni_(1-δ)O (0≦δ) having the NaCl-type crystal structure. Thus, active material particles having a surface layer portion including Ta and Ni_(1-δ)O (0≦δ) was obtained. The presence of Ni_(1-δ)O (0≦δ) having the NaCl-type crystal structure was confirmed by XRD measurement or XENES measurement. In Examples below as well, presence of Ni_(1-δ)O (0≦δ) in the active material particles was confirmed by XRD measurement or XENES measurement.

(iii) Positive Electrode Preparation

The obtained active material particles in an amount of 1 kg was stirred with a double-armed kneader along with 0.5 kg of PVDF#1320 (an N-methyl-2-pyrrolidone (NMP) solution including 12 wt % of PVDF) manufactured by Kureha Corporation, 40 g of acetylene black, and an appropriate amount of NMP, to prepare a positive electrode material mixture paste. This paste was applied on both sides of aluminum foil with a thickness of 20 μm, dried, and rolled to give a total thickness of 160 μm. Afterwards, the obtained electrode plate was cut to give a width that can be inserted to a battery case of cylindrical type 18650, to obtain a positive electrode.

(iv) Negative Electrode Preparation

A negative electrode material mixture paste was prepared by stirring 3 kg of artificial graphite, 200 g of BM-400B (dispersion including 40 wt % of modified styrene-butadiene rubber) manufactured by Zeon Corporation, 50 g of carboxymethylcellulose (CMC), and an appropriate amount of water with a double-armed kneader. This paste was applied on both sides of copper foil with a thickness of 12 μm, dried, and rolled to give a total thickness of 160 μm. Afterwards, the obtained electrode plate was cut to give a width that can be inserted to the above battery case, to obtain a negative electrode.

(v) Battery Assembly

Description is given by referring to FIG. 2. First, a positive electrode 21 and a negative electrode 22 were wound with a separator 23 interposed therebetween, to form an electrode assembly. For the separator 23, a composite film (2300 manufactured by Celgard KK, thickness of 25 μm) comprising polyethylene and polypropylene was used.

To the positive electrode 21 and the negative electrode 22, a positive electrode lead 24 and a negative electrode lead 25 of nickel were attached, respectively. An upper insulating plate 26 and a lower insulating plate 27 were placed on the top face and the bottom face of the electrode assembly, respectively, and inserted into a battery case 28, and further, 5 g of a non-aqueous electrolyte was injected into the battery case 28.

For the non-aqueous electrolyte, to a solvent mixture of ethylene carbonate and methylethyl carbonate with a volume ratio of 10:30, LiPF₆ was dissolved with a concentration of 1.5 mol/L and used.

Afterwards, a positive electrode terminal 30 of a sealing plate 29 for sealing the opening of the battery case 28, and the positive electrode lead 24 were brought into conduction, and the opening was sealed. A cylindrical type 18650 lithium secondary battery was thus completed. This battery was named as Example Battery A1.

Example Battery A2

Battery A2 was made in the same manner as Battery A1 except that the amount of tantalum pentaethoxide dissolved in 10 L of ethanol was changed to 2.0 mol % relative to the first lithium-nickel composite oxide.

Example Battery A3

Battery A3 was made in the same manner as Battery A1, except that in the first step of synthesizing active material particles, a solution dissolving aluminum (Al: element M) triisopropoxide in 10 L of isopropanol was used instead of the ethanol solution of tantalum pentaethoxide. The amount of aluminum triisopropoxide dissolved was set to 0.5 mol % relative to the first lithium-nickel composite oxide.

Example Battery A4

Battery A4 was made in the same manner as Battery A3, except that the amount of aluminum triisopropoxide dissolved in 10 L of isopropanol was changed to 2.0 mol % relative to the first lithium-nickel composite oxide.

Example Battery A5

Battery A5 was made in the same manner as Battery A1, except that in the first step of synthesizing active material particles, a solution dissolving zirconium (Zr: element M) tetra-n-butoxide in 10 L of butanol was used instead of the ethanol solution of tantalum pentaethoxide. The amount of zirconium tetra-n-butoxide dissolved was set to 0.5 mol % relative to the first lithium-nickel composite oxide.

Example Battery A6

Battery A6 was made in the same manner as Battery A5, except that the amount of zirconium tetra-n-butoxide dissolved in 10 L of butanol was changed to 2.0 mol % relative to the first lithium-nickel composite oxide.

Example Battery A7

Battery A7 was made in the same manner as Battery A1, except that in the first step of synthesizing active material particles, a solution dissolving magnesium acetate (Mg: element M) in 10 L of ethanol was used instead of the ethanol solution of tantalum pentaethoxide. The amount of magnesium acetate was set to 0.5 mol % relative to the first lithium-nickel composite oxide.

Example Battery A8

Battery A8 was made in the same manner as Battery A7, except that amount of magnesium acetate dissolved in 10 L of ethanol was changed to 2.0 mol % relative to the first lithium-nickel composite oxide.

Example Battery A9

Battery A9 was made in the same manner as Battery A1, except that in the first step of synthesizing active material particles, a solution dissolving indium nitrate (In: element M) in 10 L of ethanol was used instead of the ethanol solution of tantalum pentaethoxide. The amount of indium nitrate dissolved was set to 0.5 mol % relative to the first lithium-nickel composite oxide.

Example Battery A10

Battery A10 was made in the same manner as Battery A9, except that the amount of indium nitrate dissolved in 10 L of ethanol was changed to 2.0 mol % relative to the first lithium-nickel composite oxide.

Example Battery A11

In the first step of synthesizing active material particles, 2 kg of the first lithium-nickel composite oxide was dispersed in 10 L of an aqueous solution of sodium hydroxide with pH13 instead of the ethanol solution of tantalum pentaethoxide. Tin sulfate (Sn: element M) in an amount of 0.5 mol % relative to the first lithium-nickel composite oxide was dissolved in 100 g of distilled water. To a mixed solution of the first lithium-nickel composite oxide and the aqueous solution of sodium hydroxide, an aqueous solution of tin sulfate was dropped for 10 minutes. Afterwards, Battery A11 was made in the same manner as Battery A1, except that the stirring was carried out for 3 hours at 100° C.

Example Battery A12

Battery A12 was made in the same manner as Battery A11, except that the amount of tin sulfate dissolved in 100 g of distilled water was changed to 2.0 mol % relative to the first lithium-nickel composite oxide.

Example Battery A13

Battery A13 was made in the same manner as Battery A11, except that tin sulfate was changed to manganese sulfate (Mn: element M).

Example Battery A14

Battery A14 was made in the same manner as Battery A12, except that tin sulfate was changed to manganese sulfate.

Example Battery A15

Battery A15 was made in the same manner as Battery A11, except that tin sulfate was changed to boric acid (B: element M).

Example Battery A16

Battery A16 was made in the same manner as Battery A12, except that tin sulfate was changed to boric acid.

Example Battery A17

Battery A17 was made in the same manner as Battery A11, except that tin sulfate was changed to sodium tungstate (W: element M).

Example Battery A18

Battery A18 was made in the same manner as Battery A12, except that tin sulfate was changed to sodium tungstate.

Example Battery A19

Battery A19 was made in the same manner as Battery A11, except that tin sulfate was changed to niobium pentachloride (Nb: element M).

Example Battery A20

Battery A20 was made in the same manner as Battery A12, except that tin sulfate was changed to niobium pentachloride.

Example Battery A21

Battery A21 was made in the same manner as Battery A11, except that tin sulfate was changed to ammonium heptamolybdate (Mo: element M).

Example Battery A22

Battery A22 was made in the same manner as Battery A12, except that tin sulfate was changed to ammonium heptamolybdate.

Example Batteries A23 to A33

Batteries A23 to A33 were made in the same manner as Batteries 1A, 3A, 5A, 7A, 9A, 11A, 13A, 15A, 17A, 19A, and 21A, except that the respective amount of tantalum pentaethoxide, aluminum triisopropoxide, zirconium tetra-n-butoxide, magnesium acetate, indium nitrate, tin sulfate, manganese sulfate, boric acid, sodium tungstate, niobium pentachloride, and ammonium heptamolybdate was set to 2.5 mol % relative to the first lithium-nickel composite oxide.

Example Batteries A34 to A44

Batteries A34 to A44 were made in the same manner as Batteries 1A, 3A, 5A, 7A, 9A, 11A, 13A, 15A, 17A, 19A, and 21A, except that in the second step of synthesizing the active material particles, the environment for allowing the first lithium-nickel composite oxide carrying element M (powder after drying) to stand was changed to an environment with a temperature of 60° C. and a humidity of 55%.

Comparative Example Batteries a1 to a11

Batteries a1 to a11 were made in the same manner as Batteries 1A, 3A, 5A, 7A, 9A, 11A, 13A, 15A, 17A, 19A, and 21A, respectively, except that in the second step of synthesizing the active material particles, the environment for allowing the first lithium-nickel composite oxide carrying element M (powder after drying) to stand was changed to an environment with a temperature of 25° C. and a humidity of 20%.

No Ni_(1-δ)O (0≦δ) production was confirmed in XRD measurement on active material particles in each battery.

Comparative Example Batteries a12 to a22

Batteries a12 to a22 were made in the same manner as Batteries 1A, 3A, 5A, 7A, 9A, 11A, 13A, 15A, 17A, 19A, and 21A, except that in the third step of synthesizing the active material particles, the atmosphere of preliminarily baking the first lithium-nickel composite oxide with NiOOH formed on the surface thereof was changed from the dry air atmosphere to an atmosphere of 100% oxygen (pressure 101 KPa).

No Ni_(1-δ)O production was confirmed in XRD measurement on the active material particles of each battery. Preliminarily baking in highly oxidizing atmosphere probably causes Ni_(1-δ)O (0≦δ), i.e., a reduction product, not to be produced.

Comparative Example Batteries a23 to a33

Batteries a23 to a33 were made in the same manner as Batteries 1A, 3A, 5A, 7A, 9A, 11A, 13A, 15A, 17A, 19A, and 21A, except that in the third step of synthesizing the active material particles, the atmospheres of the main baking and of the following annealing of the first lithium-nickel composite oxide with NiOOH formed on the surface thereof were changed from the atmosphere of 100% oxygen to a dry air atmosphere (humidity 19%, pressure 101 KPa).

No Ni_(1-δ)O (0≦δ) production was confirmed in XRD measurement on the active material particles of each battery. The main baking in a dry air atmosphere probably causes no Ni_(1-δ)O (0≦δ) production, but causes the active material itself to be changed into a different phase.

Comparative Example Battery a34

Battery a34 was made in the same manner as Battery A1, except that in the synthesizing of the active material particles, the first step was not carried out, and the first lithium-nickel composite oxide was allowed to stand as is in the second step for 24 hours, under an environment with a temperature of 25° C. and a humidity of 55%.

NiO production was confirmed in an analysis on the active material particles.

Comparative Example Battery a35

Battery a35 was made in the same manner as Battery A1, except that the first lithium-nickel composite oxide to which 0.5 mol % of NiO powder was added was used as the positive electrode active material.

Comparative Example Battery a36

A first lithium-nickel composite oxide was heat-treated under an atmosphere of a mixed gas of a 95:5 molar ratio nitrogen and hydrogen at 400° C. for 6 hours, to form a reduced layer including Ni and Co having a low valence on the surface of the first lithium-nickel composite oxide. Battery a36 was made in the same manner as Battery A1, except that a first lithium-nickel composite oxide with the thus obtained reduced layer was used as the positive electrode active material.

Comparative Example Battery a37

Battery a37 was made in the same manner as Battery A1, except that a first lithium-nickel composite oxide not containing element M and Ni_(1-δ)O (0≦δ) was used as is as the positive electrode active material.

[Evaluation 1]

Example Batteries A1 to A44 and Comparative Example Batteries a1 to a37 were evaluated with the method below. The results are shown in Tables 1A and 1B.

TABLE 1A First Lithium-Nickel Composite Oxide: LiNi_(0.80)Co_(0.15)Al_(0.05)O₂ Internal Short Circuit Safety Environment to Discharge 60° C.-Crush Speed be Allowed to Performance 5 mm/Sec Stand Discharge Highest Amount Temperature · Preliminary Main Baking- 400 mA 4000 mA Temperature Battery Added Humidity Baking Annealing at 0° C. at 0° C. Reached No Element M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) (° C.) Ex. A1 Ta 0.5 25 · 55 Dry Air Oxygen 1980 1900 70 Ex. A2 2.0 1985 1900 75 Ex. A3 Al 0.5 1985 1905 70 Ex. A4 2.0 1990 1905 71 Ex. A5 Zr 0.5 1990 1910 65 Ex. A6 2.0 1990 1910 65 Ex. A7 Mg 0.5 1995 1915 70 Ex. A8 2.0 1992 1920 72 Ex. A9 In 0.5 1990 1925 71 Ex. A10 2.0 1995 1920 65 Ex. A11 Sn 0.5 1990 1910 72 Ex. A12 2.0 1989 1905 71 Ex. A13 Mn 0.5 1990 1900 65 Ex. A14 2.0 1991 1900 70 Ex. A15 B 0.5 1991 1900 72 Ex. A16 2.0 1990 1905 75 Ex. A17 W 0.5 1990 1902 74 Ex. A18 2.0 1992 1910 72 Ex. A19 Nb 0.5 1980 1905 70 Ex. A20 2.0 1990 1905 71 Ex. A21 Mo 0.5 1990 1905 65 Ex. A22 2.0 1990 1900 70 Ex. A23 Ta 2.5 1990 1800 70 Ex. A24 Al 1992 1810 70 Ex. A25 Zr 1980 1800 70 Ex. A26 Mg 1985 1805 75 Ex. A27 In 1982 1800 78 Ex. A28 Sn 1990 1805 68 Ex. A29 Mn 1990 1802 70 Ex. A30 B 1989 1800 71 Ex. A31 W 1990 1810 69 Ex. A32 Nb 1990 1900 70 Ex. A33 Mo 1992 1900 72 Ex. A34 Ta 0.5 60 · 55 1800 1701 70 Ex. A35 Al 1805 1700 68 Ex. A36 Zr 1810 1710 69 Ex. A37 Mg 1820 1715 71 Ex. A38 In 1800 1700 71 Ex. A39 Sn 1805 1700 72 Ex. A40 Mn 1807 1702 68 Ex. A41 B 1800 1710 67 Ex. A42 W 1800 1705 70 Ex. A43 Nb 1800 1700 70 Ex. A44 Mo 1805 1700 68

TABLE 1B First Lithium-Nickel Composite Oxide: LiNi_(0.80)Co_(0.15)Al_(0.05)O₂ Internal Short Circuit Safety Environment to Discharge 60° C.-Crush Speed be Allowed to Performance 5 mm/Sec Stand Discharge Highest Amount Temperature · Preliminary Main Baking- 400 mA 4000 mA Temperature Battery Added Humidity Baking Annealing at 0° C. at 0° C. Reached No Element M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) (° C.) Comp. Ex. a1 Ta 0.5 25 · 20 Dry Air Oxygen 1990 1920 120 Comp. Ex. a2 Al 1990 1900 115 Comp. Ex. a3 Zr 1989 1900 120 Comp. Ex. a4 Mg 1990 1899 110 Comp. Ex. a5 In 1987 1890 110 Comp. Ex. a6 Sn 1985 1900 120 Comp. Ex. a7 Mn 1988 1905 115 Comp. Ex. a8 B 1990 1900 120 Comp. Ex. a9 W 1985 1900 125 Comp. Ex. a10 Nb 1992 1902 110 Comp. Ex. a11 Mo 1990 1900 122 Comp. Ex. a12 Ta 25 · 55 Oxygen 1982 1910 117 Comp. Ex. a13 Al 1980 1910 122 Comp. Ex. a14 Zr 1985 1915 125 Comp. Ex. a15 Mg 1990 1915 120 Comp. Ex. a16 In 1995 1910 118 Comp. Ex. a17 Sn 1995 1900 115 Comp. Ex. a18 Mn 1990 1905 112 Comp. Ex. a19 B 1990 1910 110 Comp. Ex. a20 W 1992 1908 115 Comp. Ex. a21 Nb 1990 1905 110 Comp. Ex. a22 Mo 1989 1900 120 Comp. Ex. a23 Ta Dry Air Dry Air 1990 1910 120 Comp. Ex. a24 Al 1985 1905 109 Comp. Ex. a25 Zr 1988 1905 105 Comp. Ex. a26 Mg 1986 1900 100 Comp. Ex. a27 In 1990 1915 102 Comp. Ex. a28 Sn 1970 1900 100 Comp. Ex. a29 Mn 1985 1905 106 Comp. Ex. a30 B 1985 1900 107 Comp. Ex. a31 W 1990 1910 100 Comp. Ex. a32 Nb 1991 1904 100 Comp. Ex. a33 Mo 1990 1905 105 Comp. Ex. a34 Not — 25 · 55 Oxygen 1800 1700 75 Added Comp. Ex. a35 Not 0.5 Not Carried Out 1995 1910 110 Comp. Ex. a36 Added — Mixed Gas of Nitrogen:Hydrogen = 95:5 1990 1910 115 (molar ratio) treatment at 400° C. for 6 hours Comp. Ex. a37 Not Carried Out 1995 1915 140 (Discharge Performance)

Each battery was preliminary charged and discharged twice, and then stored under an environment of 40° C. for 2 days. Afterwards, the following two patterns of charging and discharging were carried out for each battery. The battery designed capacity was 2000 mAh.

First Pattern

(1) Constant Current Charging (20° C.): 1400 mA (End Voltage 4.2 V)

(2) Constant Voltage Charging (20° C.): 4.2 V (End Current 100 mA)

(3) Constant Current Discharging (0° C.): 400 mA (End Voltage 3 V)

Second Pattern

(1) Constant Current Charging (20° C.): 1400 mA (end voltage 4.2 V)

(2) Constant Voltage Charging (20° C.): 4.2 V (end current 100 mA)

(3) Constant Current Discharging (0° C.): 4000 mA (end voltage 3 V)

The discharge capacities obtained in the first and the second pattern are shown in Tables 1A and 1B.

(Safety)

A battery crush test was carried out under an environment of 60° C. for evaluating safety upon internal short-circuit occurrence. First, the following charging was carried out for those batteries after the discharge performance evaluation under an environment of 20° C. The battery designed capacity was 2000 mAh.

(1) Constant Current Charging: 1400 mA (end voltage 4.25 V)

(2) Constant Voltage Charging: 4.25 V (end current 100 mA)

An iron rod with a 10 mm diameter was thrust at a speed of 5 mm/sec from a side face of the charged battery under an environment of 60° C. to break the battery. The temperatures reached at the broken portion of the battery after 90 seconds are shown in Tables 1A and 1B.

The evaluation results are shown below.

In Example Batteries A1 to A22, in which the active material particle surface layer portion includes element M and Ni_(1-δ)O (0≦δ≦0.1), and the amount of element M is 0.5 mol % or 2 mol % relative to the first lithium-nickel composite oxide, the degree of the heat generation was quite small in the crush test. The discharge capacity of these batteries at 0° C. in 2 CmA (4000 mAh) discharging was the same level as that of Comparative Example Battery a37 using the first lithium-nickel composite oxide as is.

In Example Batteries A23 to A33, in which the amount of element M relative to the lithium composite oxide is 2.5 mol %, the discharge capacity in 2 CmA (4000 mAh) discharging at 0° C. declined. The compound of element M included in the surface layer portion of the first lithium-nickel composite oxide was electrochemically inactive and thus probably became resistance.

Example Batteries A34 to A44, in which a condition for allowing the first lithium-nickel composite oxide carrying element M before baking to stand was changed to give high temperature, the discharge capacity tended to be low. This is probably because the portions other than the side reaction active points of the first lithium-nickel composite oxide were changed to Ni_(1-δ)O.

In Comparative Example Battery a34, in which the first lithium-nickel composite oxide was baked after being allowed to stand under an environment of a temperature of 25° C. and a humidity of 55% for 24 hours and used without carrying element M, the discharge capacity was not sufficient. This is probably because the absence of element M at the surface caused the first lithium-nickel composite oxide to deteriorate.

In Comparative Example Batteries a1 to a11, in which a condition for the first lithium-nickel composite oxide carrying element M before baking to stand was changed to give low humidity, and Comparative Example Batteries a12 to a33, in which the baking atmosphere was changed, a great amount of heat was generated in the crush test. This is probably because Ni_(1-δ)O (0≦δ), which inactivates the side reaction active points of the first lithium-nickel composite oxide was not produced.

In Comparative Example Battery a35 as well, in which the first lithium-nickel composite oxide with NiO added was used for the positive electrode active material, since the side reaction active points did not disappear, a great amount of heat generated in the crush test.

In Comparative Example Battery a36, in which the lithium composite oxide surface with the reduced layer formed on the surface thereof was used as the positive electrode active material, the discharge capacity with 2 CmA (4000 mAh) at 0° C. was insufficient. This is probably because the first lithium-nickel composite oxide surface was covered with Ni or Co having a low oxidation number and low electrochemical activity.

EXAMPLE 2

A first lithium-nickel composite oxide having a composition of LiNi_(0.9)Co_(0.07)Al_(0.03)O₂ was obtained by using nickel sulfate, cobalt sulfate, and aluminum sulfate so that a molar ratio of Ni atoms, Co atoms, and Al atoms was 90:7:3 upon synthesizing the first lithium-nickel composite oxide. Example Batteries B1 to B44 and Comparative Example Batteries b1 to b37 were made in the same manner as Example Batteries A1 to A44 and Comparative Example Batteries a1 to a37, respectively, except that this first lithium-nickel composite oxide was used as the raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Tables 2A and 2B.

TABLE 2A First Lithium-Nickel Composite Oxide: LiNi_(0.90)Co_(0.07)Al_(0.03)O₂ Internal Short Circuit Safety Environment to Discharge 60° C.-Crush Speed be Allowed to Performance 5 mm/Sec Stand Discharge Highest Amount Temperature · Preliminary Main Baking- 400 mA 4000 mA Temperature Battery Added Humidity Baking Annealing at 0° C. at 0° C. Reached No Element M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) (° C.) Ex. B1 Ta 0.5 25 · 55 Dry Air Oxygen 1485 1460 65 Ex. B2 2.0 1490 1455 65 Ex. B3 Al 0.5 1480 1462 70 Ex. B4 2.0 1475 1460 65 Ex. B5 Zr 0.5 1470 1460 70 Ex. B6 2.0 1475 1458 71 Ex. B7 Mg 0.5 1470 1455 65 Ex. B8 2.0 1470 1460 65 Ex. B9 In 0.5 1480 1455 71 Ex. B10 2.0 1485 1457 65 Ex. B11 Sn 0.5 1480 1456 65 Ex. B12 2.0 1480 1450 65 Ex. B13 Mn 0.5 1482 1460 71 Ex. B14 2.0 1485 1462 72 Ex. B15 B 0.5 1490 1465 72 Ex. B16 2.0 1475 1455 74 Ex. B17 W 0.5 1475 1455 72 Ex. B18 2.0 1480 1460 75 Ex. B19 Nb 0.5 1480 1460 70 Ex. B20 2.0 1482 1460 72 Ex. B21 Mo 0.5 1490 1465 72 Ex. B22 2.0 1485 1460 70 Ex. B23 Ta 2.5 1480 1330 70 Ex. B24 Al 1490 1330 70 Ex. B25 Zr 1485 1335 70 Ex. B26 Mg 1486 1332 75 Ex. B27 In 1490 1332 70 Ex. B28 Sn 1488 1335 70 Ex. B29 Mn 1480 1335 70 Ex. B30 B 1485 1330 75 Ex. B31 W 1490 1330 69 Ex. B32 Nb 1485 1325 71 Ex. B33 Mo 1490 1330 72 Ex. B34 Ta 0.5 60 · 55 1300 1200 75 Ex. B35 Al 1305 1205 72 Ex. B36 Zr 1302 1200 75 Ex. B37 Mg 1300 1200 74 Ex. B38 In 1305 1205 72 Ex. B39 Sn 1302 1207 75 Ex. B40 Mn 1300 1202 74 Ex. B41 B 1300 1205 70 Ex. B42 W 1305 1205 71 Ex. B43 Nb 1300 1200 72 Ex. B44 Mo 1302 1205 71

TABLE 2B First Lithium-Nickel Composite Oxide: LiNi_(0.90)Co_(0.07)Al_(0.03)O₂ Internal Short Circuit Safety Environment to Discharge 60° C.-Crush Speed be Allowed to Performance 5 mm/Sec Stand Discharge Highest Amount Temperature · Preliminary Main Baking- 400 mA 4000 mA Temperature Battery Added Humidity Baking Annealing at 0° C. at 0° C. Reached No Element M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) (° C.) Comp. Ex. b1 Ta 0.5 25 · 20 Dry Air Oxygen 1490 1455 120 Comp. Ex. b2 Al 1492 1456 106 Comp. Ex. b3 Zr 1495 1457 107 Comp. Ex. b4 Mg 1487 1455 100 Comp. Ex. b5 In 1488 1450 117 Comp. Ex. b6 Sn 1489 1460 115 Comp. Ex. b7 Mn 1490 1465 120 Comp. Ex. b8 B 1492 1466 118 Comp. Ex. b9 W 1496 1455 115 Comp. Ex. b10 Nb 1492 1460 120 Comp. Ex. b11 Mo 1495 1450 120 Comp. Ex. b12 Ta 25 · 55 Oxygen 1495 1450 112 Comp. Ex. b13 Al 1497 1460 106 Comp. Ex. b14 Zr 1490 1460 115 Comp. Ex. b15 Mg 1485 1450 120 Comp. Ex. b16 In 1489 1450 118 Comp. Ex. b17 Sn 1480 1455 115 Comp. Ex. b18 Mn 1485 1452 112 Comp. Ex. b19 B 1480 1456 110 Comp. Ex. b20 W 1490 1462 115 Comp. Ex. b21 Nb 1492 1460 112 Comp. Ex. b22 Mo 1495 1462 110 Comp. Ex. b23 Ta Dry Air Dry Air 1490 1462 120 Comp. Ex. b24 Al 1490 1465 109 Comp. Ex. b25 Zr 1485 1466 105 Comp. Ex. b26 Mg 1488 1468 100 Comp. Ex. b27 In 1488 1468 102 Comp. Ex. b28 Sn 1487 1450 100 Comp. Ex. b29 Mn 1485 1450 106 Comp. Ex. b30 B 1485 1450 107 Comp. Ex. b31 W 1490 1450 100 Comp. Ex. b32 Nb 1488 1445 105 Comp. Ex. b33 Mo 1480 1450 105 Comp. Ex. b34 Not — 25 · 55 Oxygen 1305 1202 76 Added Comp. Ex. b35 Not 0.5 Not Carried Out 1490 1460 110 Comp. Ex. b36 Added — Mixed Gas of Nitrogen:Hydrogen = 95:5 1490 1460 115 (molar ratio) treatment at 400° C. for 6 hours Comp. Ex. b37 Not Carried Out 1495 1465 130

EXAMPLE 3

A first lithium-nickel composite oxide having a composition of LiNi_(0.25)Co_(0.25)Al_(0.50)O₂ was obtained by using nickel sulfate, cobalt sulfate, and aluminum sulfate, so that a molar ratio of Ni atoms, Co atoms, and Al atoms was 25:25:50 upon synthesizing the first lithium-nickel composite oxide. Example Batteries C1 to C44 and Comparative Example Batteries c1 to c37 were made in the same manner as Example Batteries A1 to A44 and Comparative Example Batteries a1 to a37, respectively, except that this first lithium-nickel composite oxide was used as the raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Tables 3A and 3B.

TABLE 3A First Lithium-Nickel Composite Oxide: LiNi_(0.25)Co_(0.25)Al_(0.50)O₂ Internal Short Circuit Safety Environment to Discharge 60° C.-Crush Speed be Allowed to Performance 5 mm/Sec Stand Discharge Highest Amount Temperature · Preliminary Main Baking- 400 mA 4000 mA Temperature Battery Added Humidity Baking Annealing at 0° C. at 0° C. Reached No Element M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) (° C.) Ex. C1 Ta 0.5 25 · 55 Dry Air Oxygen 1485 1460 68 Ex. C2 2.0 1490 1455 64 Ex. C3 Al 0.5 1480 1462 62 Ex. C4 2.0 1475 1460 70 Ex. C5 Zr 0.5 1470 1460 70 Ex. C6 2.0 1475 1458 70 Ex. C7 Mg 0.5 1470 1455 75 Ex. C8 2.0 1470 1460 72 Ex. C9 In 0.5 1480 1455 66 Ex. C10 2.0 1485 1457 68 Ex. C11 Sn 0.5 1480 1456 64 Ex. C12 2.0 1480 1450 62 Ex. C13 Mn 0.5 1482 1460 65 Ex. C14 2.0 1485 1462 59 Ex. C15 B 0.5 1490 1465 60 Ex. C16 2.0 1475 1455 61 Ex. C17 W 0.5 1475 1455 65 Ex. C18 2.0 1480 1460 67 Ex. C19 Nb 0.5 1480 1455 66 Ex. C20 2.0 1485 1457 68 Ex. C21 Mo 0.5 1480 1456 64 Ex. C22 2.0 1480 1450 62 Ex. C23 Ta 2.5 1480 1350 68 Ex. C24 Al 1490 1355 64 Ex. C25 Zr 1485 1350 65 Ex. C26 Mg 1486 1350 66 Ex. C27 In 1490 1352 69 Ex. C28 Sn 1488 1357 70 Ex. C29 Mn 1480 1356 70 Ex. C30 B 1485 1350 75 Ex. C31 W 1490 1350 69 Ex. C32 Nb 1490 1352 69 Ex. C33 Mo 1488 1357 70 Ex. C34 Ta 0.5 60 · 55 1350 1200 70 Ex. C35 Al 1355 1200 71 Ex. C36 Zr 1350 1205 72 Ex. C37 Mg 1350 1205 68 Ex. C38 In 1352 1200 69 Ex. C39 Sn 1355 1202 67 Ex. C40 Mn 1355 1205 70 Ex. C41 B 1345 1200 70 Ex. C42 W 1345 1200 75 Ex. C43 Nb 1350 1205 68 Ex. C44 Mo 1352 1200 69

TABLE 3B First Lithium-Nickel Composite Oxide: LiNi_(0.25)Co_(0.25)Al_(0.50)O₂ Internal Short Circuit Safety Environment to Discharge 60° C.-Crush Speed be Allowed to Performance 5 mm/Sec Stand Discharge Highest Amount Temperature · Preliminary Main Baking- 400 mA 4000 mA Temperature Battery Added Humidity Baking Annealing at 0° C. at 0° C. Reached No Element M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) (° C.) Comp. Ex. c1 Ta 0.5 25 · 20 Dry Air Oxygen 1490 1450 110 Comp. Ex. c2 Al 1492 1456 105 Comp. Ex. c3 Zr 1495 1457 107 Comp. Ex. c4 Mg 1487 1455 109 Comp. Ex. c5 In 1488 1450 110 Comp. Ex. c6 Sn 1489 1460 105 Comp. Ex. c7 Mn 1490 1465 108 Comp. Ex. c8 B 1492 1466 110 Comp. Ex. c9 W 1496 1455 115 Comp. Ex. c10 Nb 1488 1450 110 Comp. Ex. c11 Mo 1489 1460 105 Comp. Ex. c12 Ta 25 · 55 Oxygen 1495 1450 112 Comp. Ex. c13 Al 1497 1460 110 Comp. Ex. c14 Zr 1490 1460 110 Comp. Ex. c15 Mg 1485 1450 115 Comp. Ex. c16 In 1489 1450 120 Comp. Ex. c17 Sn 1480 1455 120 Comp. Ex. c18 Mn 1485 1452 118 Comp. Ex. c19 B 1480 1456 116 Comp. Ex. c20 W 1490 1462 119 Comp. Ex. c21 Nb 1480 1455 120 Comp. Ex. c22 Mo 1485 1452 118 Comp. Ex. c23 Ta Dry Air Dry Air 1490 1462 120 Comp. Ex. c24 Al 1490 1465 120 Comp. Ex. c25 Zr 1485 1466 120 Comp. Ex. c26 Mg 1488 1468 115 Comp. Ex. c27 In 1488 1468 112 Comp. Ex. c28 Sn 1487 1450 116 Comp. Ex. c29 Mn 1485 1450 117 Comp. Ex. c30 B 1485 1450 118 Comp. Ex. c31 W 1490 1450 120 Comp. Ex. c32 Nb 1487 1450 116 Comp. Ex. c33 Mo 1485 1450 117 Comp. Ex. c34 Not — 25 · 55 Oxygen 1340 1180 77 Added Comp. Ex. c35 Not 0.5 Not Carried Out 1490 1460 120 Comp. Ex. c36 Added — Mixed Gas of Nitrogen:Hydrogen = 95:5 1490 1460 120 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. c37 Not Carried Out 1495 1465 130

EXAMPLE 4

A first lithium-nickel composite oxide having a composition of LiNi_(0.25)Co_(0.50)Al_(0.25)O₂ was obtained by using nickel sulfate, cobalt sulfate, and aluminum sulfate, so that a molar ratio of Ni atoms, Co atoms, and Al atoms was 25:50:25 upon synthesizing the first lithium-nickel composite oxide. Example Batteries D1 to D44 and Comparative Example Batteries d1 to d37 were made in the same manner as Example Batteries A1 to A44 and Comparative Example Batteries a1 to a37, respectively, except that this first lithium-nickel composite oxide was used as the raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Tables 4A and 4B.

TABLE 4A First Lithium-Nickel Composite Oxide: LiNi_(0.25)Co_(0.50)Al_(0.25)O₂ Internal Short Circuit Safety Environment to Discharge 60° C.-Crush Speed be Allowed to Performance 5 mm/Sec Stand Discharge Highest Amount Temperature · Preliminary Main Baking- 400 mA 4000 mA Temperature Battery Added Humidity Baking Annealing at 0° C. at 0° C. Reached No Element M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) (° C.) Ex. D1 Ta 0.5 25 · 55 Dry Air Oxygen 1880 1810 60 Ex. D2 2.0 1890 1815 65 Ex. D3 Al 0.5 1885 1812 64 Ex. D4 2.0 1884 1810 61 Ex. D5 Zr 0.5 1882 1810 65 Ex. D6 2.0 1880 1815 65 Ex. D7 Mg 0.5 1892 1815 70 Ex. D8 2.0 1892 1810 70 Ex. D9 In 0.5 1880 1812 68 Ex. D10 2.0 1880 1816 67 Ex. D11 Sn 0.5 1880 1810 65 Ex. D12 2.0 1889 1815 65 Ex. D13 Mn 0.5 1889 1812 70 Ex. D14 2.0 1887 1812 64 Ex. D15 B 0.5 1888 1812 65 Ex. D16 2.0 1888 1810 65 Ex. D17 W 0.5 1888 1810 70 Ex. D18 2.0 1888 1810 72 Ex. D19 Nb 0.5 1880 1810 65 Ex. D20 2.0 1889 1815 65 Ex. D21 Mo 0.5 1889 1812 70 Ex. D22 2.0 1887 1812 64 Ex. D23 Ta 2.5 1889 1600 68 Ex. D24 Al 1890 1610 65 Ex. D25 Zr 1892 1605 65 Ex. D26 Mg 1895 1605 62 Ex. D27 In 1897 1601 62 Ex. D28 Sn 1897 1605 72 Ex. D29 Mn 1890 1610 70 Ex. D30 B 1890 1610 70 Ex. D31 W 1885 1600 70 Ex. D32 Nb 1897 1601 62 Ex. D33 Mo 1897 1605 72 Ex. D34 Ta 0.5 60 · 55 1620 1500 68 Ex. D35 Al 1620 1505 67 Ex. D36 Zr 1625 1510 70 Ex. D37 Mg 1630 1510 71 Ex. D38 In 1635 1500 71 Ex. D39 Sn 1620 1500 71 Ex. D40 Mn 1625 1505 72 Ex. D41 B 1620 1502 68 Ex. D42 W 1625 1500 69 Ex. D43 Nb 1620 1500 71 Ex. D44 Mo 1625 1505 72

TABLE 4B First Lithium-Nickel Composite Oxide: LiNi_(0.25)Co_(0.50)Al_(0.25)O₂ Internal Short Circuit Safety Environment to Discharge 60° C.-Crush Speed be Allowed to Performance 5 mm/Sec Stand Discharge Highest Amount Temperature · Preliminary Main Baking- 400 mA 4000 mA Temperature Battery Added Humidity Baking Annealing at 0° C. at 0° C. Reached No Element M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) (° C.) Comp. Ex. d1 Ta 0.5 25 · 20 Dry Air Oxygen 1880 1812 120 Comp. Ex. d2 Al 1885 1812 115 Comp. Ex. d3 Zr 1885 1815 111 Comp. Ex. d4 Mg 1888 1815 120 Comp. Ex. d5 In 1887 1815 112 Comp. Ex. d6 Sn 1889 1812 115 Comp. Ex. d7 Mn 1890 1810 118 Comp. Ex. d8 B 1892 1810 118 Comp. Ex. d9 W 1891 1810 120 Comp. Ex. d10 Nb 1889 1812 115 Comp. Ex. d11 Mo 1890 1810 118 Comp. Ex. d12 Ta 25 · 55 Oxygen 1891 1815 110 Comp. Ex. d13 Al 1890 1812 112 Comp. Ex. d14 Zr 1890 1812 112 Comp. Ex. d15 Mg 1890 1812 118 Comp. Ex. d16 In 1890 1812 118 Comp. Ex. d17 Sn 1890 1815 115 Comp. Ex. d18 Mn 1890 1810 120 Comp. Ex. d19 B 1888 1811 120 Comp. Ex. d20 W 1887 1811 120 Comp. Ex. d21 Nb 1890 1815 115 Comp. Ex. d22 Mo 1890 1810 120 Comp. Ex. d23 Ta Dry Air Dry Air 1885 1816 110 Comp. Ex. d24 Al 1890 1817 110 Comp. Ex. d25 Zr 1890 1818 105 Comp. Ex. d26 Mg 1888 1818 108 Comp. Ex. d27 In 1887 1817 107 Comp. Ex. d28 Sn 1886 1817 109 Comp. Ex. d29 Mn 1892 1818 110 Comp. Ex. d30 B 1892 1817 110 Comp. Ex. d31 W 1892 1818 112 Comp. Ex. d32 Nb 1886 1817 109 Comp. Ex. d33 Mo 1892 1818 110 Comp. Ex. d34 Not — 25 · 55 Oxygen 1615 1480 71 Added Comp. Ex. d35 Not 0.5 Not Carried Out 1890 1818 112 Comp. Ex. d36 Added — Mixed Gas of Nitrogen:Hydrogen = 95:5 1888 1818 115 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. d37 Not Carried Out 1892 1815 120

EXAMPLE 5

A first lithium-nickel composite oxide having a composition of LiNi_(0.90)Co_(0.10)O₂ was obtained by using nickel sulfate and cobalt sulfate without using aluminum sulfate, so that a molar ratio of Ni atoms and Co atoms was 90:10 upon synthesizing the first lithium-nickel composite oxide. Example Batteries E1 to E44 and Comparative Example Batteries e1 to e37 were made in the same manner as Example Batteries A1 to A44 and Comparative Example Batteries a1 to a37, respectively, except that this first lithium-nickel composite oxide was used as the raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Tables 5A and 5B.

TABLE 5A First Lithium-Nickel Composite Oxide: LiNi_(0.90)Co_(0.10)O₂ Internal Short Circuit Safety Environment to Discharge 60° C.-Crush Speed be Allowed to Performance 5 mm/Sec Stand Discharge Highest Amount Temperature · Preliminary Main Baking- 400 mA 4000 mA Temperature Battery Added Humidity Baking Annealing at 0° C. at 0° C. Reached No Element M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) (° C.) Ex. E1 Ta 0.5 25 · 55 Dry Air Oxygen 2000 1900 65 Ex. E2 2.0 2005 1905 70 Ex. E3 Al 0.5 2004 1902 68 Ex. E4 2.0 2002 1900 62 Ex. E5 Zr 0.5 2000 1902 62 Ex. E6 2.0 2000 1900 64 Ex. E7 Mg 0.5 1999 1900 65 Ex. E8 2.0 1998 1905 70 Ex. E9 In 0.5 2002 1900 71 Ex. E10 2.0 2000 1900 75 Ex. E11 Sn 0.5 2000 1905 64 Ex. E12 2.0 2005 1904 68 Ex. E13 Mn 0.5 2000 1902 62 Ex. E14 2.0 2004 1902 65 Ex. E15 B 0.5 2002 1900 62 Ex. E16 2.0 1999 1910 67 Ex. E17 W 0.5 2002 1910 70 Ex. E18 2.0 2000 1915 72 Ex. E19 Nb 0.5 2002 1900 71 Ex. E20 2.0 2000 1900 75 Ex. E21 Mo 0.5 2004 1902 65 Ex. E22 2.0 2002 1900 62 Ex. E23 Ta 2.5 2000 1700 69 Ex. E24 Al 2002 1702 68 Ex. E25 Zr 1999 1710 67 Ex. E26 Mg 1998 1715 70 Ex. E27 In 2002 1705 60 Ex. E28 Sn 2000 1705 60 Ex. E29 Mn 2000 1700 62 Ex. E30 B 2005 1702 65 Ex. E31 W 2004 1700 64 Ex. E32 Nb 2002 1705 60 Ex. E33 Mo 2005 1702 65 Ex. E34 Ta 0.5 60 · 55 1750 1610 70 Ex. E35 Al 1750 1612 72 Ex. E36 Zr 1755 1600 65 Ex. E37 Mg 1760 1620 68 Ex. E38 In 1765 1625 67 Ex. E39 Sn 1760 1630 62 Ex. E40 Mn 1762 1625 65 Ex. E41 B 1758 1620 67 Ex. E42 W 1757 1615 70 Ex. E43 Nb 1760 1630 62 Ex. E44 Mo 1758 1620 67

TABLE 5B First Lithium-Nickel Composite Oxide: LiNi_(0.90)Co_(0.10)O₂ Internal Short Circuit Safety Environment to Discharge 60° C.-Crush Speed be Allowed to Performance 5 mm/Sec Stand Discharge Highest Amount Temperature · Preliminary Main Baking- 400 mA 4000 mA Temperature Battery Added Humidity Baking Annealing at 0° C. at 0° C. Reached No Element M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) (° C.) Comp. Ex. e1 Ta 0.5 25 · 20 Dry Air Oxygen 2004 1900 118 Comp. Ex. e2 Al 2005 1900 119 Comp. Ex. e3 Zr 2000 1905 120 Comp. Ex. e4 Mg 2000 1905 115 Comp. Ex. e5 In 2002 1902 114 Comp. Ex. e6 Sn 2000 1902 112 Comp. Ex. e7 Mn 2003 1902 110 Comp. Ex. e8 B 2005 1900 120 Comp. Ex. e9 W 2005 1905 115 Comp. Ex. e10 Nb 2003 1902 110 Comp. Ex. e11 Mo 2002 1902 114 Comp. Ex. e12 Ta 25 · 55 Oxygen 2000 1902 116 Comp. Ex. e13 Al 2000 1902 114 Comp. Ex. e14 Zr 2005 1905 118 Comp. Ex. e15 Mg 2000 1900 117 Comp. Ex. e16 In 1999 1905 116 Comp. Ex. e17 Sn 1998 1902 112 Comp. Ex. e18 Mn 1997 1903 118 Comp. Ex. e19 B 1999 1904 116 Comp. Ex. e20 W 2000 1904 115 Comp. Ex. e21 Nb 1997 1903 118 Comp. Ex. e22 Mo 1999 1905 116 Comp. Ex. e23 Ta Dry Air Dry Air 2002 1900 120 Comp. Ex. e24 Al 2002 1901 120 Comp. Ex. e25 Zr 2004 1900 110 Comp. Ex. e26 Mg 2003 1900 100 Comp. Ex. e27 In 2000 1905 100 Comp. Ex. e28 Sn 2000 1904 110 Comp. Ex. e29 Mn 2000 1902 105 Comp. Ex. e30 B 2003 1900 120 Comp. Ex. e31 W 2005 1900 120 Comp. Ex. e32 Nb 2000 1902 105 Comp. Ex. e33 Mo 2003 1900 120 Comp. Ex. e34 Not — 25 · 55 Oxygen 1750 1600 72 Added Comp. Ex. e35 Not 0.5 Not Carried Out 2000 1900 114 Comp. Ex. e36 Added — Mixed Gas of Nitrogen:Hydrogen = 95:5 2005 1901 112 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. e37 Not Carried Out 2005 1905 120

EXAMPLE 6

A first lithium-nickel composite oxide having a composition of LiNi_(0.50)Co_(0.50)O₂ was obtained by using nickel sulfate and cobalt sulfate without using aluminum sulfate so that a molar ratio of Ni atoms and Co atoms was 50:50 upon synthesizing the first lithium-nickel composite oxide. Example Batteries F1 to F44 and Comparative Example Batteries f1 to f37 were made in the same manner as Example Batteries A1 to A44 and Comparative Example Batteries a1 to a37, respectively, except that this first lithium-nickel composite oxide was used as the raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Tables 6A and 6B.

TABLE 6A First Lithium-Nickel Composite Oxide: LiNi_(0.50)Co_(0.50)O₂ Environment Discharge Internal Short to be Allowed Performance Circuit Safety to Stand Discharge 60° C. · Crush Amount Temperature · Preliminary Main Baking · 400 mA 4000 mA Speed 5 mm/Sec Battery Element Added Humidity Baking Annealing at 0° C. at 0° C. Highest Temperature No M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) Reached (° C.) Ex. F1 Ta 0.5 25 · 55 Dry Air Oxygen 2000 1900 60 Ex. F2 2.0 2000 1905 62 Ex. F3 Al 0.5 2004 1902 65 Ex. F4 2.0 2002 1900 61 Ex. F5 Zr 0.5 2000 1902 70 Ex. F6 2.0 2000 1900 65 Ex. F7 Mg 0.5 1999 1900 61 Ex. F8 2.0 1998 1905 62 Ex. F9 In 0.5 2002 1900 64 Ex. F10 2.0 2000 1900 68 Ex. F11 Sn 0.5 2000 1905 66 Ex. F12 2.0 2005 1904 62 Ex. F13 Mn 0.5 2000 1902 61 Ex. F14 2.0 2004 1902 62 Ex. F15 B 0.5 2002 1900 65 Ex. F16 2.0 1999 1910 64 Ex. F17 W 0.5 2002 1910 66 Ex. F18 2.0 2000 1915 65 Ex. F19 Nb 0.5 2000 1905 66 Ex. F20 2.0 2002 1900 65 Ex. F21 Mo 0.5 2000 1900 65 Ex. F22 2.0 2004 1902 65 Ex. F23 Ta 2.5 2000 1700 69 Ex. F24 Al 2002 1702 67 Ex. F25 Zr 1999 1710 65 Ex. F26 Mg 1998 1715 68 Ex. F27 In 2002 1705 64 Ex. F28 Sn 2000 1705 66 Ex. F29 Mn 2000 1700 65 Ex. F30 B 2005 1702 64 Ex. F31 W 2004 1700 65 Ex. F32 Nb 2002 1705 64 Ex. F33 Mo 2000 1700 65 Ex. F34 Ta 0.5 60 · 55 1780 1600 62 Ex. F35 Al 1770 1620 65 Ex. F36 Zr 1720 1650 63 Ex. F37 Mg 1780 1680 67 Ex. F38 In 1760 1630 64 Ex. F39 Sn 1790 1620 62 Ex. F40 Mn 1760 1680 65 Ex. F41 B 1750 1650 65 Ex. F42 W 1780 1650 65 Ex. F43 Nb 1780 1680 67 Ex. F44 Mo 1790 1620 62

TABLE 6B First Lithium-Nickel Composite Oxide: LiNi_(0.50)Co_(0.50)O₂ Environment Discharge Internal Short to be Allowed Performance Circuit Safety to Stand Discharge 60° C. · Crush Amount Temperature · Preliminary Main Baking · 400 mA 4000 mA Speed 5 mm/Sec Battery Element Added Humidity Baking Annealing at 0° C. at 0° C. Highest Temperature No M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) Reached (° C.) Comp. Ex. f1 Ta 0.5 25 · 20 Dry Air Oxygen 2004 1900 120 Comp. Ex. f2 Al 2005 1900 110 Comp. Ex. f3 Zr 2000 1905 115 Comp. Ex. f4 Mg 2000 1905 112 Comp. Ex. f5 In 2002 1902 114 Comp. Ex. f6 Sn 2000 1902 112 Comp. Ex. f7 Mn 2003 1902 112 Comp. Ex. f8 B 2005 1900 125 Comp. Ex. f9 W 2005 1905 120 Comp. Ex. f10 Nb 2002 1902 114 Comp. Ex. f11 Mo 2003 1902 112 Comp. Ex. f12 Ta 25 · 55 Oxygen 2000 1902 116 Comp. Ex. f13 Al 2000 1902 118 Comp. Ex. f14 Zr 2005 1905 110 Comp. Ex. f15 Mg 2000 1900 112 Comp. Ex. f16 In 1999 1905 115 Comp. Ex. f17 Sn 1998 1902 115 Comp. Ex. f18 Mn 1997 1903 118 Comp. Ex. f19 B 1999 1904 117 Comp. Ex. f20 W 2000 1904 119 Comp. Ex. f21 Nb 1999 1905 115 Comp. Ex. f22 Mo 1997 1903 118 Comp. Ex. f23 Ta Dry Air Dry Air 2002 1900 110 Comp. Ex. f24 Al 2002 1901 110 Comp. Ex. f25 Zr 2004 1900 115 Comp. Ex. f26 Mg 2003 1900 117 Comp. Ex. f27 In 2000 1905 118 Comp. Ex. f28 Sn 2000 1904 116 Comp. Ex. f29 Mn 2000 1902 120 Comp. Ex. f30 B 2003 1900 120 Comp. Ex. f31 W 2005 1900 115 Comp. Ex. f32 Nb 2000 1902 120 Comp. Ex. f33 Mo 2000 1904 116 Comp. Ex. f34 Not Added — 25 · 55 Oxygen 1710 1600  60 Comp. Ex. f35 Not Added 0.5 Not Carried Out 2000 1900 112 Comp. Ex. f36 — Mixed Gas of Nitrogen:Hydrogen = 95:5 2005 1901 110 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. f37 Not Carried Out 2005 1905 130

EXAMPLE 7

Nickel sulfate, cobalt sulfate, and aluminum sulfate were mixed so that a molar ratio of Ni atoms, Co atoms, and Al atoms was 80:15:3. The obtained mixture in an amount of 3.2 kg was dissolved in 10 L of water, to obtain a raw material solution. To the raw material solution, 400 g of sodium hydroxide was added to form a precipitate. The precipitate was sufficiently washed with water and dried, to obtain a coprecipitated hydroxide.

To 3 kg of the obtained coprecipitated hydroxide of Ni—Co—Al, 853 g of lithium hydroxide and 378 g of manganese nitrate were mixed. The obtained mixture was baked at a synthesizing temperature of 750° C. for 10 hours under an atmosphere with an oxygen partial pressure of 0.5 atm, to obtain a first lithium-nickel composite oxide including Al and Mn as element Me (composition: LiNi_(0.8)Cu_(0.15)Al_(0.03)Mn_(0.02)O₂).

Example Batteries G1 to G44 and Comparative Example Batteries g1 to g37 were made in the same manner as Example Batteries A1 to A44 and Comparative Example Batteries a1 to a37, respectively, except that this first lithium-nickel composite oxide was used as the raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Tables 7A and 7B.

TABLE 7A First Lithium-Nickel Composite Oxide: LiNi_(0.80)Co_(0.15)Al_(0.03)Mn_(0.02)O₂ Environment Discharge Internal Short to be Allowed Performance Circuit Safety to Stand Discharge 60° C. · Crush Amount Temperature · Preliminary Main Baking · 400 mA 4000 mA Speed 5 mm/Sec Battery Element Added Humidity Baking Annealing at 0° C. at 0° C. Highest Temperature No M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) Reached (° C.) Ex. G1 Ta 0.5 25 · 55 Dry Air Oxygen 2002 1905 62 Ex. G2 2.0 2004 1900 65 Ex. G3 Al 0.5 2005 1902 66 Ex. G4 2.0 2002 1905 60 Ex. G5 Zr 0.5 2000 1900 68 Ex. G6 2.0 2000 1900 68 Ex. G7 Mg 0.5 2000 1900 64 Ex. G8 2.0 2002 1900 64 Ex. G9 In 0.5 2004 1900 64 Ex. G10 2.0 2003 1902 66 Ex. G11 Sn 0.5 2002 1900 66 Ex. G12 2.0 2004 1904 66 Ex. G13 Mn 0.5 2000 1910 60 Ex. G14 2.0 2000 1915 60 Ex. G15 B 0.5 2000 1900 61 Ex. G16 2.0 2002 1910 61 Ex. G17 W 0.5 2000 1910 62 Ex. G18 2.0 2004 1915 62 Ex. G19 Nb 0.5 2001 1900 68 Ex. G20 2.0 2002 1905 68 Ex. G21 Mo 0.5 2000 1902 67 Ex. G22 2.0 2000 1902 67 Ex. G23 Ta 2.5 2002 1705 64 Ex. G24 Al 2004 1715 66 Ex. G25 Zr 2004 1705 65 Ex. G26 Mg 2004 1715 65 Ex. G27 In 2004 1702 64 Ex. G28 Sn 2000 1700 64 Ex. G29 Mn 2005 1700 66 Ex. G30 B 2005 1702 65 Ex. G31 W 2005 1700 65 Ex. G32 Nb 2000 1700 65 Ex. G33 Mo 2000 1705 64 Ex. G34 Ta 0.5 60 · 55 1760 1660 65 Ex. G35 Al 1750 1680 65 Ex. G36 Zr 1760 1678 64 Ex. G37 Mg 1780 1670 67 Ex. G38 In 1750 1655 62 Ex. G39 Sn 1750 1675 60 Ex. G40 Mn 1780 1677 60 Ex. G41 B 1760 1682 62 Ex. G42 W 1780 1685 62 Ex. G43 Nb 1780 1678 65 Ex. G44 Mo 1790 1679 65

TABLE 7B First Lithium-Nickel Composite Oxide: LiNi_(0.80)Co_(0.15)Al_(0.03)Mn_(0.02)O₂ Environment Discharge Internal Short to be Allowed Performance Circuit Safety to Stand Discharge 60° C. · Crush Amount Temperature · Preliminary Main Baking · 400 mA 4000 mA Speed 5 mm/Sec Battery Element Added Humidity Baking Annealing at 0° C. at 0° C. Highest Temperature No M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) Reached (° C.) Comp. Ex. g1 Ta 0.5 25 · 20 Dry Air Oxygen 2002 1905 125 Comp. Ex. g2 Al 2004 1902 115 Comp. Ex. g3 Zr 2002 1900 110 Comp. Ex. g4 Mg 2002 1900 110 Comp. Ex. g5 In 2000 1905 120 Comp. Ex. g6 Sn 2000 1900 120 Comp. Ex. g7 Mn 2004 1902 120 Comp. Ex. g8 B 2004 1905 110 Comp. Ex. g9 W 2002 1900 120 Comp. Ex. g10 Nb 2004 1905 110 Comp. Ex. g11 Mo 2004 1905 110 Comp. Ex. g12 Ta 25 · 55 Oxygen 2000 1900 115 Comp. Ex. g13 Al 2000 1900 120 Comp. Ex. g14 Zr 2004 1902 110 Comp. Ex. g15 Mg 2005 1900 120 Comp. Ex. g16 In 2000 1900 120 Comp. Ex. g17 Sn 2005 1902 120 Comp. Ex. g18 Mn 2004 1905 120 Comp. Ex. g19 B 2002 1902 120 Comp. Ex. g20 W 2002 1904 120 Comp. Ex. g21 Nb 2000 1900 115 Comp. Ex. g22 Mo 2000 1900 118 Comp. Ex. g23 Ta Dry Air Dry Air 2004 1902 115 Comp. Ex. g24 Al 2005 1900 118 Comp. Ex. g25 Zr 2005 1905 116 Comp. Ex. g26 Mg 2000 1902 117 Comp. Ex. g27 In 2002 1904 120 Comp. Ex. g28 Sn 2002 1905 120 Comp. Ex. g29 Mn 2002 1900 110 Comp. Ex. g30 B 2004 1902 110 Comp. Ex. g31 W 2004 1904 115 Comp. Ex. g32 Nb 2004 1900 110 Comp. Ex. g33 Mo 2004 1900 115 Comp. Ex. g34 Not Added — 25 · 55 Oxygen 1720 1605  65 Comp. Ex. g35 Not Added 0.5 Not Carried Out 2002 1905 120 Comp. Ex. g36 — Mixed Gas of Nitrogen:Hydrogen = 95:5 2004 1900 115 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. g37 Not Carried Out 2004 1902 127

EXAMPLE 8

To 3 kg of a coprecipitated hydroxide of Ni—Co—Al prepared in the same manner as Example 7, 853 g of lithium hydroxide and 378 g of magnesium sulfate were mixed. The obtained mixture was baked at a synthesizing temperature of 750° C. for 10 hours under an atmosphere with an oxygen partial pressure of 0.5 atm, to obtain a first lithium-nickel composite oxide including Al and Mg as element Me (composition: LiNi_(0.8)Co_(0.15)Al_(0.03)Mg_(0.02)O₂).

Example Batteries H1 to H44 and Comparative Example Batteries h1 to h37 were made in the same manner as Example Batteries A1 to A44 and Comparative Example Batteries a1 to a37, respectively, except that this first lithium-nickel composite oxide was used as the raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Tables 8A and 8B.

TABLE 8A First Lithium-Nickel Composite Oxide: LiNi_(0.80)Co_(0.15)Al_(0.03)Mg_(0.02)O₂ Environment Discharge Internal Short to be Allowed Performance Circuit Safety to Stand Discharge 60° C. · Crush Amount Temperature · Preliminary Main Baking · 400 mA 4000 mA Speed 5 mm/Sec Battery Element Added Humidity Baking Annealing at 0° C. at 0° C. Highest Temperature No M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) Reached (° C.) Ex. H1 Ta 0.5 25 · 55 Dry Air Oxygen 2005 1904 67 Ex. H2 2.0 2004 1905 64 Ex. H3 Al 0.5 2003 1904 65 Ex. H4 2.0 2000 1903 64 Ex. H5 Zr 0.5 2002 1902 64 Ex. H6 2.0 2004 1904 68 Ex. H7 Mg 0.5 2006 1900 61 Ex. H8 2.0 2004 1903 62 Ex. H9 In 0.5 2003 1905 67 Ex. H10 2.0 2008 1902 64 Ex. H11 Sn 0.5 2004 1904 62 Ex. H12 2.0 2006 1905 62 Ex. H13 Mn 0.5 2004 1904 63 Ex. H14 2.0 2005 1905 64 Ex. H15 B 0.5 2002 1906 67 Ex. H16 2.0 2000 1903 62 Ex. H17 W 0.5 2001 1901 69 Ex. H18 2.0 2003 1901 67 Ex. H19 Nb 0.5 2004 1904 65 Ex. H20 2.0 2005 1902 61 Ex. H21 Mo 0.5 2006 1905 62 Ex. H22 2.0 2004 1903 64 Ex. H23 Ta 2.5 2002 1705 65 Ex. H24 Al 2000 1702 63 Ex. H25 Zr 2006 1704 64 Ex. H26 Mg 2004 1705 66 Ex. H27 In 2005 1706 66 Ex. H28 Sn 2004 1709 66 Ex. H29 Mn 2003 1705 67 Ex. H30 B 2005 1701 62 Ex. H31 W 2004 1700 63 Ex. H32 Nb 2006 1705 64 Ex. H33 Mo 2004 1704 65 Ex. H34 Ta 0.5 60 · 55 1780 1610 62 Ex. H35 Al 1778 1620 60 Ex. H36 Zr 1778 1640 60 Ex. H37 Mg 1772 1670 62 Ex. H38 In 1772 1650 62 Ex. H39 Sn 1777 1620 63 Ex. H40 Mn 1778 1640 62 Ex. H41 B 1776 1650 61 Ex. H42 W 1777 1670 63 Ex. H43 Nb 1775 1640 64 Ex. H44 Mo 1778 1650 62

TABLE 8B First Lithium-Nickel Composite Oxide: LiNi_(0.80)Co_(0.15)Al_(0.03)Mg_(0.02)O₂ Environment Discharge Internal Short to be Allowed Performance Circuit Safety to Stand Discharge 60° C. · Crush Amount Temperature · Preliminary Main Baking · 400 mA 4000 mA Speed 5 mm/Sec Battery Element Added Humidity Baking Annealing at 0° C. at 0° C. Highest Temperature No M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) Reached (° C.) Comp. Ex. h1 Ta 0.5 25 · 20 Dry Air Oxygen 2000 1904 125 Comp. Ex. h2 Al 2002 1902 120 Comp. Ex. h3 Zr 2005 1904 124 Comp. Ex. h4 Mg 2004 1905 123 Comp. Ex. h5 In 2003 1904 125 Comp. Ex. h6 Sn 2005 1906 124 Comp. Ex. h7 Mn 2004 1900 126 Comp. Ex. h8 B 2001 1905 120 Comp. Ex. h9 W 2003 1904 125 Comp. Ex. h10 Nb 2006 1902 121 Comp. Ex. h11 Mo 2005 1904 123 Comp. Ex. h12 Ta 25 · 55 Oxygen 2003 1903 118 Comp. Ex. h13 Al 2003 1904 115 Comp. Ex. h14 Zr 2006 1905 114 Comp. Ex. h15 Mg 2004 1904 116 Comp. Ex. h16 In 2000 1903 114 Comp. Ex. h17 Sn 2000 1904 118 Comp. Ex. h18 Mn 2005 1900 119 Comp. Ex. h19 B 2003 1900 116 Comp. Ex. h20 W 2001 1900 117 Comp. Ex. h21 Nb 2005 1905 112 Comp. Ex. h22 Mo 2004 1904 120 Comp. Ex. h23 Ta Dry Air Dry Air 2003 1902 115 Comp. Ex. h24 Al 2005 1902 110 Comp. Ex. h25 Zr 2006 1903 115 Comp. Ex. h26 Mg 2003 1904 114 Comp. Ex. h27 In 2004 1905 118 Comp. Ex. h28 Sn 2000 1904 119 Comp. Ex. h29 Mn 2000 1904 119 Comp. Ex. h30 B 2005 1900 116 Comp. Ex. h31 W 2003 1901 114 Comp. Ex. h32 Nb 2006 1900 115 Comp. Ex. h33 Mo 2004 1900 118 Comp. Ex. h34 Not Added — 25 · 55 Oxygen 1712 1605  62 Comp. Ex. h35 Not Added 0.5 Not Carried Out 2005 1904 115 Comp. Ex. h36 — Mixed Gas of Nitrogen:Hydrogen = 95:5 2002 1900 118 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. h37 Not Carried Out 2002 1900 125

EXAMPLE 9

To 3 kg of a coprecipitated hydroxide of Ni—Co—Al prepared in the same manner as Example 7, 853 g of lithium hydroxide and 378 g of calcium hydroxide were mixed. The obtained mixture was baked under an atmosphere with an oxygen partial pressure of 0.5 atm at a synthesizing temperature of 750° C. for 10 hours, to obtain a first lithium-nickel composite oxide including Al and Ca as element Me (composition: LiNi_(0.8)Co_(0.15)Al_(0.03)Ca_(0.02)O₂).

Example Batteries I1 to I44 and Comparative Example Batteries i1 to i37 were made in the same manner as Example Batteries A1 to A44 and Comparative Example Batteries a1 to a37, respectively, except that this first lithium-nickel composite oxide was used as the raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Tables 9A and 9B.

TABLE 9A First Lithium-Nickel Composite Oxide: LiNi_(0.80)Co_(0.15)Al_(0.03)Ca_(0.02)O₂ Environment Discharge Internal Short to be Allowed Performance Circuit Safety to Stand Discharge 60° C. · Crush Amount Temperature · Preliminary Main Baking · 400 mA 4000 mA Speed 5 mm/Sec Battery Element Added Humidity Baking Annealing at 0° C. at 0° C. Highest Temperature No M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) Reached (° C.) Ex. I1 Ta 0.5 25 · 55 Dry Air Oxygen 2005 1905 62 Ex. I2 2.0 2000 1902 64 Ex. I3 Al 0.5 2002 1900 65 Ex. I4 2.0 2005 1905 66 Ex. I5 Zr 0.5 2000 1904 68 Ex. I6 2.0 2002 1903 64 Ex. I7 Mg 0.5 2004 1905 62 Ex. I8 2.0 2005 1900 60 Ex. I9 In 0.5 2005 1902 64 Ex. I10 2.0 2005 1905 68 Ex. I11 Sn 0.5 2002 1904 62 Ex. I12 2.0 2004 1905 62 Ex. I13 Mn 0.5 2004 1904 64 Ex. I14 2.0 2000 1902 67 Ex. I15 B 0.5 2002 1900 68 Ex. I16 2.0 2005 1902 65 Ex. I17 W 0.5 2003 1905 62 Ex. I18 2.0 2003 1904 64 Ex. I19 Nb 0.5 2004 1904 62 Ex. I20 2.0 2000 1900 62 Ex. I21 Mo 0.5 2002 1905 61 Ex. I22 2.0 2005 1900 62 Ex. I23 Ta 2.5 2000 1705 67 Ex. I24 Al 2005 1705 68 Ex. I25 Zr 2000 1708 64 Ex. I26 Mg 2000 1707 68 Ex. I27 In 2005 1707 64 Ex. I28 Sn 2002 1709 65 Ex. I29 Mn 2004 1707 69 Ex. I30 B 2002 1709 67 Ex. I31 W 2000 1707 65 Ex. I32 Nb 2000 1705 64 Ex. I33 Mo 2002 1701 68 Ex. I34 Ta 0.5 60 · 55 1785 1650 65 Ex. I35 Al 1775 1670 64 Ex. I36 Zr 1725 1680 65 Ex. I37 Mg 1770 1670 67 Ex. I38 In 1770 1675 67 Ex. I39 Sn 1780 1672 62 Ex. I40 Mn 1750 1678 64 Ex. I41 B 1740 1682 64 Ex. I42 W 1770 1668 68 Ex. I43 Nb 1770 1680 68 Ex. I44 Mo 1790 1678 62

TABLE 9B First Lithium-Nickel Composite Oxide: LiNi_(0.80)Co_(0.15)Al_(0.03)Ca_(0.02)O₂ Environment Discharge Internal Short to be Allowed Performance Circuit Safety to Stand Discharge 60° C. · Crush Amount Temperature · Preliminary Main Baking · 400 mA 4000 mA Speed 5 mm/Sec Battery Element Added Humidity Baking Annealing at 0° C. at 0° C. Highest Temperature No M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) Reached (° C.) Comp. Ex. i1 Ta 0.5 25 · 20 Dry Air Oxygen 2002 1902 125 Comp. Ex. i2 Al 2004 1905 124 Comp. Ex. i3 Zr 2002 1900 123 Comp. Ex. i4 Mg 2002 1904 123 Comp. Ex. i5 In 2000 1905 124 Comp. Ex. i6 Sn 2005 1900 120 Comp. Ex. i7 Mn 2004 1900 118 Comp. Ex. i8 B 2005 1905 119 Comp. Ex. i9 W 2004 1902 117 Comp. Ex. i10 Nb 2004 1905 121 Comp. Ex. i11 Mo 2004 1905 120 Comp. Ex. i12 Ta 25 · 55 Oxygen 2002 1900 118 Comp. Ex. i13 Al 2002 1904 120 Comp. Ex. i14 Zr 2002 1904 122 Comp. Ex. i15 Mg 2000 1905 123 Comp. Ex. i16 In 2000 1904 124 Comp. Ex. i17 Sn 2002 1902 125 Comp. Ex. i18 Mn 2000 1900 125 Comp. Ex. i19 B 2000 1901 124 Comp. Ex. i20 W 2002 1902 119 Comp. Ex. i21 Nb 2000 1903 119 Comp. Ex. i22 Mo 2000 1903 120 Comp. Ex. i23 Ta Dry Air Dry Air 2005 1905 118 Comp. Ex. i24 Al 2004 1902 112 Comp. Ex. i25 Zr 2002 1905 114 Comp. Ex. i26 Mg 2000 1904 118 Comp. Ex. i27 In 2003 1905 116 Comp. Ex. i28 Sn 2003 1906 117 Comp. Ex. i29 Mn 2005 1905 118 Comp. Ex. i30 B 2004 1903 118 Comp. Ex. i31 W 2005 1900 119 Comp. Ex. i32 Nb 2002 1900 121 Comp. Ex. i33 Mo 2000 1902 122 Comp. Ex. i34 Not Added — 25 · 55 Oxygen 1715 1605  59 Comp. Ex. i35 Not Added 0.5 Not Carried Out 2005 1904 120 Comp. Ex. i36 — Mixed Gas of Nitrogen:Hydrogen = 95:5 2000 1900 115 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. i37 Not Carried Out 2000 1905 129

EXAMPLE 10

To 3 kg of a coprecipitated hydroxide of Ni—Co—Al prepared in the same manner as Example 7, 853 g of lithium hydroxide and 378 g of titanium sulfate were mixed. The obtained mixture was baked under an atmosphere with an oxygen partial pressure of 0.5 atm, and at a synthesizing temperature of 750° C. for 10 hours, to obtain a first lithium-nickel composite oxide including Al and Ti as element Me (composition: LiNi_(0.8)Co_(0.15)Al_(0.03)Ti_(0.02)O₂).

Example Batteries J1 to J44 and Comparative Example Batteries j1 to j37 were made in the same manner as Example Batteries A1 to A44 and Comparative Example Batteries a1 to a37, respectively, except that this first lithium-nickel composite oxide was used as the raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Tables 10A and 10B.

TABLE 10A Lithium Composite Oxide: LiNi_(0.80)Co_(0.15)Al_(0.03)Ti_(0.02)O₂ Environment Discharge Internal Short to be Allowed Performance Circuit Safety to Stand Discharge 60° C. · Crush Amount Temperature · Preliminary Main Baking · 400 mA 4000 mA Speed 5 mm/Sec Battery Element Added Humidity Baking Annealing at 0° C. at 0° C. Highest Temperature No M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) Reached (° C.) Ex. J1 Ta 0.5 25 · 55 Dry Air Oxygen 2000 1905 64 Ex. J2 2.0 2004 1902 62 Ex. J3 Al 0.5 2005 1903 64 Ex. J4 2.0 2002 1904 65 Ex. J5 Zr 0.5 2000 1903 62 Ex. J6 2.0 2003 1902 62 Ex. J7 Mg 0.5 2005 1902 60 Ex. J8 2.0 2000 1904 60 Ex. J9 In 0.5 2000 1902 62 Ex. J10 2.0 2002 1903 62 Ex. J11 Sn 0.5 2001 1904 61 Ex. J12 2.0 2006 1905 63 Ex. J13 Mn 0.5 2003 1900 64 Ex. J14 2.0 2004 1902 61 Ex. J15 B 0.5 2000 1903 62 Ex. J16 2.0 2002 1900 60 Ex. J17 W 0.5 2002 1900 60 Ex. J18 2.0 2004 1905 63 Ex. J19 Nb 0.5 2002 1904 65 Ex. J20 2.0 2003 1900 64 Ex. J21 Mo 0.5 2006 1902 62 Ex. J22 2.0 2005 1900 62 Ex. J23 Ta 2.5 2002 1705 60 Ex. J24 Al 2004 1705 64 Ex. J25 Zr 2005 1708 64 Ex. J26 Mg 2002 1710 68 Ex. J27 In 2000 1708 66 Ex. J28 Sn 2002 1704 67 Ex. J29 Mn 2004 1702 68 Ex. J30 B 2006 1700 64 Ex. J31 W 2003 1705 65 Ex. J32 Nb 2002 1702 64 Ex. J33 Mo 2002 1705 68 Ex. J34 Ta 0.5 60 · 55 1780 1615 65 Ex. J35 Al 1778 1625 64 Ex. J36 Zr 1779 1637 62 Ex. J37 Mg 1775 1650 68 Ex. J38 In 1777 1625 67 Ex. J39 Sn 1778 1620 65 Ex. J40 Mn 1777 1650 62 Ex. J41 B 1778 1630 64 Ex. J42 W 1780 1640 68 Ex. J43 Nb 1781 1650 67 Ex. J44 Mo 1782 1640 68

TABLE 10B First Lithium-Nickel Composite Oxide: LiNi_(0.80)Co_(0.15)Al_(0.03)Ti_(0.02)O₂ Environment Discharge Internal Short to be Allowed Performance Circuit Safety to Stand Discharge 60° C. · Crush Amount Temperature · Preliminary Main Baking · 400 mA 4000 mA Speed 5 mm/Sec Battery Element Added Humidity Baking Annealing at 0° C. at 0° C. Highest Temperature No M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) Reached (° C.) Comp. Ex. j1 Ta 0.5 25 · 20 Dry Air Oxygen 2000 1904 117 Comp. Ex. j2 Al 2004 1905 115 Comp. Ex. j3 Zr 2002 1904 120 Comp. Ex. j4 Mg 2005 1900 120 Comp. Ex. j5 In 2004 1905 115 Comp. Ex. j6 Sn 2000 1900 117 Comp. Ex. j7 Mn 2002 1902 117 Comp. Ex. j8 B 2003 1902 115 Comp. Ex. j9 W 2005 1900 117 Comp. Ex. j10 Nb 2004 1905 112 Comp. Ex. j11 Mo 2005 1900 115 Comp. Ex. j12 Ta 25 · 55 Oxygen 2002 1904 114 Comp. Ex. j13 Al 2002 1900 115 Comp. Ex. j14 Zr 2000 1903 118 Comp. Ex. j15 Mg 2005 1903 119 Comp. Ex. j16 In 2002 1902 117 Comp. Ex. j17 Sn 2004 1902 111 Comp. Ex. j18 Mn 2003 1900 112 Comp. Ex. j19 B 2002 1905 115 Comp. Ex. j20 W 2002 1900 110 Comp. Ex. j21 Nb 2000 1900 120 Comp. Ex. j22 Mo 2000 1900 125 Comp. Ex. j23 Ta Dry Air Dry Air 2004 1904 111 Comp. Ex. j24 Al 2005 1900 117 Comp. Ex. j25 Zr 2006 1905 115 Comp. Ex. j26 Mg 2004 1900 111 Comp. Ex. j27 In 2002 1900 112 Comp. Ex. j28 Sn 2002 1905 115 Comp. Ex. j29 Mn 2000 1904 111 Comp. Ex. j30 B 2003 1902 111 Comp. Ex. j31 W 2005 1900 115 Comp. Ex. j32 Nb 2002 1904 117 Comp. Ex. j33 Mo 2002 1907 117 Comp. Ex. j34 Not Added — 25 · 55 Oxygen 1710 1607  67 Comp. Ex. j35 Not Added 0.5 Not Carried Out 2005 1907 117 Comp. Ex. j36 — Mixed Gas of Nitrogen:Hydrogen = 95:5 2004 1907 115 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. j37 Not Carried Out 2002 1907 124

The results in Table 2A to 10A, and in Tables 2B to 10B showed almost the same tendency with the case of Example 1.

COMPARATIVE EXAMPLE 1

A first lithium-nickel composite oxide having a composition of LiNi_(0.20)Co_(0.50)Al_(0.30)O₂ was obtained by using nickel sulfate, cobalt sulfate, and aluminum sulfate so that a molar ratio of Ni atoms, Co atoms, and Al atoms was 20:50:30 upon synthesizing the first lithium-nickel composite oxide. Comparative Example Batteries k1 to k81 were prepared in the same manner as Example Batteries A1 to 44 and Comparative Example Batteries a1 to 37, respectively, except that this first lithium-nickel composite oxide was used as the raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Tables 11A and 11B.

TABLE 11A First Lithium-Nickel Composite Oxide: LiNi_(0.20)Co_(0.50)Al_(0.30)O₂ Internal Short Circuit Safety 60° C.- Environment Discharge Crush Speed to be Allowed Performance 5 mm/Sec to Stand Discharge Highest Amount Temperature · Preliminary Main Baking- 400 mA 4000 mA Temperature Battery Added Humidity Baking Annealing at 0° C. at 0° C. Reached No Element M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) (° C.) Comp. Ex. k1 Ta 0.5 25 · 55 Dry Air Oxygen 1800 1710 117 Comp. Ex. k2 2.0 1805 1720 115 Comp. Ex. k3 Al 0.5 1804 1715 117 Comp. Ex. k4 2.0 1805 1710 112 Comp. Ex. k5 Zr 0.5 1802 1710 115 Comp. Ex. k6 2.0 1800 1712 117 Comp. Ex. k7 Mg 0.5 1810 1715 120 Comp. Ex. k8 2.0 1805 1709 118 Comp. Ex. k9 In 0.5 1800 1708 117 Comp. Ex. k10 2.0 1800 1710 110 Comp. Ex. k11 Sn 0.5 1801 1710 112 Comp. Ex. k12 2.0 1810 1712 113 Comp. Ex. k13 Mn 0.5 1805 1715 115 Comp. Ex. k14 2.0 1805 1715 110 Comp. Ex. k15 B 0.5 1800 1715 120 Comp. Ex. k16 2.0 1805 1712 118 Comp. Ex. k17 W 0.5 1805 1710 117 Comp. Ex. k18 2.0 1810 1715 117 Comp. Ex. k19 Nb 0.5 1815 1710 115 Comp. Ex. k20 2.0 1805 1705 115 Comp. Ex. k21 Mo 0.5 1805 1700 120 Comp. Ex. k22 2.0 1815 1715 120 Comp. Ex. k23 Ta 2.5 1800 1530 117 Comp. Ex. k24 Al 1800 1535 120 Comp. Ex. k25 Zr 1805 1540 118 Comp. Ex. k26 Mg 1807 1535 119 Comp. Ex. k27 In 1806 1530 115 Comp. Ex. k28 Sn 1805 1530 116 Comp. Ex. k29 Mn 1807 1532 112 Comp. Ex. k30 B 1806 1533 100 Comp. Ex. k31 W 1800 1540 100 Comp. Ex. k32 Nb 1805 1530 120 Comp. Ex. k33 Mo 1806 1530 110 Comp. Ex. k34 Ta 0.5 60 · 55 1805 1620 105 Comp. Ex. k35 Al 1803 1625 100 Comp. Ex. k36 Zr 1804 1610 110 Comp. Ex. k37 Mg 1805 1605 112 Comp. Ex. k38 In 1818 1605 105 Comp. Ex. k39 Sn 1810 1600 106 Comp. Ex. k40 Mn 1810 1620 110 Comp. Ex. k41 B 1805 1622 110 Comp. Ex. k42 W 1805 1600 105 Comp. Ex. k43 Nb 1800 1600 120 Comp. Ex. k44 Mo 1804 1610 116

TABLE 11B First Lithium-Nickel Composite Oxide: LiNi_(0.20)Co_(0.50)Al_(0.30)O₂ Internal Short Circuit Safety 60° C.- Environment Discharge Crush Speed to be Allowed Performance 5 mm/Sec to Stand Discharge Highest Amount Temperature · Preliminary Main Baking- 400 mA 4000 mA Temperature Battery Added Humidity Baking Annealing at 0° C. at 0° C. Reached No Element M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) (° C.) Comp. Ex. k45 Ta 0.5 25 · 20 Dry Air Oxygen 1800 1710 120 Comp. Ex. k46 Al 1805 1715 120 Comp. Ex. k47 Zr 1804 1710 115 Comp. Ex. k48 Mg 1802 1712 115 Comp. Ex. k49 In 1802 1712 110 Comp. Ex. k50 Sn 1805 1710 120 Comp. Ex. k51 Mn 1804 1715 120 Comp. Ex. k52 B 1802 1710 122 Comp. Ex. k53 W 1802 1715 125 Comp. Ex. k54 Nb 1805 1711 118 Comp. Ex. k55 Mo 1805 1710 118 Comp. Ex. k56 Ta 25 · 55 Oxygen 1805 1717 122 Comp. Ex. k57 Al 1802 1717 123 Comp. Ex. k58 Zr 1803 1717 124 Comp. Ex. k59 Mg 1805 1715 122 Comp. Ex. k60 In 1805 1710 120 Comp. Ex. k61 Sn 1802 1712 125 Comp. Ex. k62 Mn 1810 1715 124 Comp. Ex. k63 B 1805 1712 125 Comp. Ex. k64 W 1807 1710 123 Comp. Ex. k65 Nb 1800 1710 122 Comp. Ex. k66 Mo 1800 1710 122 Comp. Ex. k67 Ta Dry Air Dry Air 1801 1710 115 Comp. Ex. k68 Al 1805 1710 115 Comp. Ex. k69 Zr 1807 1712 112 Comp. Ex. k70 Mg 1801 1715 110 Comp. Ex. k71 In 1805 1715 111 Comp. Ex. k72 Sn 1806 1712 112 Comp. Ex. k73 Mn 1800 1712 117 Comp. Ex. k74 B 1800 1710 115 Comp. Ex. k75 W 1800 1715 115 Comp. Ex. k76 Nb 1805 1715 120 Comp. Ex. k77 Mo 1800 1718 115 Comp. Ex. k78 Not Added — 25 · 55 Oxygen 1800 1600 115 Comp. Ex. k79 Not 0.5 Not Carried Out 1802 1710 120 Comp. Ex. k80 Added — Mixed Gas of Nitrogen:Hydrogen = 95:5 1800 1710 120 treated at 400° C. for 6 hours Comp. Ex. k81 Not Carried Out 1810 1715 135

No generation of Ni_(1-δ)O was confirmed as the active material particles of each battery were analyzed. The results of Tables 7A and 7B show that in the first lithium-nickel composite oxide represented by the general formula Li_(x)Ni_(1-y-z)Co_(y)Me_(z)O₂, when y+z exceeds 0.75, Ni_(1-δ)O (0≦δ) is not generated and great amount of heat generates in the crush test.

COMPARATIVE EXAMPLE 2

Comparative Example Batteries l1 to l81 were made in the same manner as Example Batteries A1 to A44 and Comparative Example Batteries a1 to a37, respectively, except that instead of the first lithium-nickel composite oxide, LiNiO₂ was used for the raw material of the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Tables 12A and 12B.

TABLE 12A First Lithium-Nickel Composite Oxide: LiNiO₂ Internal Short Circuit Safety 60° C.- Environment Discharge Crush Speed to be Allowed Performance 5 mm/Sec to Stand Discharge Highest Amount Temperature · Preliminary Main Baking- 400 mA 4000 mA Temperature Battery Added Humidity Baking Annealing at 0° C. at 0° C. Reached No Element M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) (° C.) Comp. Ex. l1 Ta 0.5 25 · 55 Dry Air Oxygen 1800 1710 117 Comp. Ex. l2 2.0 1805 1720 115 Comp. Ex. l3 Al 0.5 1804 1715 117 Comp. Ex. l4 2.0 1805 1710 112 Comp. Ex. l5 Zr 0.5 1802 1710 115 Comp. Ex. l6 2.0 1800 1712 117 Comp. Ex. l7 Mg 0.5 1810 1715 120 Comp. Ex. l8 2.0 1805 1709 118 Comp. Ex. l9 In 0.5 1800 1708 117 Comp. Ex. l10 2.0 1800 1710 110 Comp. Ex. l11 Sn 0.5 1801 1710 112 Comp. Ex. l12 2.0 1810 1712 113 Comp. Ex. l13 Mn 0.5 1805 1715 115 Comp. Ex. l14 2.0 1805 1715 110 Comp. Ex. l15 B 0.5 1800 1715 120 Comp. Ex. l16 2.0 1805 1712 118 Comp. Ex. l17 W 0.5 1805 1710 117 Comp. Ex. l18 2.0 1810 1715 117 Comp. Ex. l19 Nb 0.5 1800 1710 120 Comp. Ex. l20 2.0 1808 1715 115 Comp. Ex. l21 Ma 0.5 1810 1715 112 Comp. Ex. l22 2.0 1810 1710 115 Comp. Ex. l23 Ta 2.5 1800 1530 117 Comp. Ex. l24 Al 1800 1535 120 Comp. Ex. l25 Zr 1805 1540 118 Comp. Ex. l26 Mg 1807 1535 119 Comp. Ex. l27 In 1806 1530 115 Comp. Ex. l28 Sn 1805 1530 116 Comp. Ex. l29 Mn 1807 1532 112 Comp. Ex. l30 B 1806 1533 100 Comp. Ex. l31 W 1800 1540 100 Comp. Ex. l32 Nb 1805 1530 120 Comp. Ex. l33 Mo 1800 1530 115 Comp. Ex. l34 Ta 0.5 60 · 55 1805 1620 105 Comp. Ex. l35 Al 1803 1625 100 Comp. Ex. l36 Zr 1804 1610 110 Comp. Ex. l37 Mg 1805 1605 112 Comp. Ex. l38 In 1818 1605 105 Comp. Ex. l39 Sn 1810 1600 106 Comp. Ex. l40 Mn 1810 1620 110 Comp. Ex. l41 B 1805 1622 110 Comp. Ex. l42 W 1805 1600 105 Comp. Ex. l43 Nb 1810 1620 115 Comp. Ex. l44 Mo 1808 1610 110

TABLE 12B First Lithium-Nickel Composite Oxide: LiNiO₂ Internal Short Circuit Safety 60° C.- Environment Discharge Crush Speed to be Allowed Performance 5 mm/Sec to Stand Discharge Highest Amount Temperature · Preliminary Main Baking- 400 mA 4000 mA Temperature Battery Added Humidity Baking Annealing at 0° C. at 0° C. Reached No Element M (mol %) (° C. · %) Atmosphere Atmosphere (mAh) (mAh) (° C.) Comp. Ex. l45 Ta 0.5 25 · 20 Dry Air Oxygen 1800 1710 120 Comp. Ex. l46 Al 1805 1715 120 Comp. Ex. l47 Zr 1804 1710 115 Comp. Ex. l48 Mg 1802 1712 115 Comp. Ex. l49 In 1802 1712 110 Comp. Ex. l50 Sn 1805 1710 120 Comp. Ex. l51 Mn 1804 1715 120 Comp. Ex. l52 B 1802 1710 122 Comp. Ex. l53 W 1802 1715 125 Comp. Ex. l54 Nb 1805 1710 125 Comp. Ex. l55 Mo 1800 1710 115 Comp. Ex. l56 Ta 25 · 55 Oxygen 1805 1717 122 Comp. Ex. l57 Al 1802 1717 123 Comp. Ex. l58 Zr 1803 1717 124 Comp. Ex. l59 Mg 1805 1715 122 Comp. Ex. l60 In 1805 1710 120 Comp. Ex. l61 Sn 1802 1712 125 Comp. Ex. l62 Mn 1810 1715 124 Comp. Ex. l63 B 1805 1712 125 Comp. Ex. l64 W 1807 1710 123 Comp. Ex. l65 Nb 1802 1710 120 Comp. Ex. l66 Mo 1805 1715 122 Comp. Ex. l67 Ta Dry Air Dry Air 1801 1710 115 Comp. Ex. l68 Al 1805 1710 115 Comp. Ex. l69 Zr 1807 1712 112 Comp. Ex. l70 Mg 1801 1715 110 Comp. Ex. l71 In 1805 1715 111 Comp. Ex. l72 Sn 1806 1712 112 Comp. Ex. l73 Mn 1800 1712 117 Comp. Ex. l74 B 1800 1710 115 Comp. Ex. l75 W 1800 1715 115 Comp. Ex. l76 Nb 1805 1710 118 Comp. Ex. l77 Mo 1800 1715 117 Comp. Ex. l78 Not Added — 25 · 55 Oxygen 1800 1600 115 Comp. Ex. l79 Not 0.5 Not Carried Out 1802 1710 120 Comp. Ex. l80 Added — Mixed Gas of Nitrogen:Hydrogen = 95:5 1800 1710 120 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. l81 Not Carried Out 1810 1715 135

The results of Tables 12A and 12B show that when LiNiO₂ was used, the discharge capacity becomes small though Ni_(1-δ)O (0≦δ) was produced.

When Z was greater than 0.5 in LiNi_(1-y-z)Co_(y)Me_(x)O₂, homogeneous solid solution could not be obtained.

EXAMPLE 11

Example Batteries M1 to M44 and Comparative Example Batteries m1 to m14 were made in the same manner as Example Batteries A1 to A44 and Comparative Example Batteries a1 to a11, a34, a36, and a37, respectively, except that the synthesizing the first lithium-nickel composite oxide and synthesizing the active material particles were carried out as below, and the evaluation was carried out in the same manner as Example 1. The results are shown in Table 13.

(i) Synthesis of First Lithium-Nickel Composite Oxide

A first lithium-nickel composite oxide including excessive lithium (Li_(1.03)Ni_(0.8)Co_(0.15)Al_(0.05)O₂) was obtained in the same manner as Example 1, except that the amount of lithium hydroxide to be mixed with 3 kg of the coprecipitated hydroxide of Ni—Co—Al was increased to 800 g.

(ii) Synthesis of Active Material Particles

In the Case of Example Batteries M1 to M44 and Comparative Example Batteries m1 to m12

Active material particles were synthesized in the same manner as Example Batteries A1 to A44 and Comparative Example Batteries a1 to a11, and a34 of Example 1, except that the third step was carried out as in below. In the third step, the first lithium-nickel composite oxide with NiOOH formed on the surface thereof was baked at 650° C. for 6 hours, under 100% oxygen atmosphere (pressure 101 KPa). By this baking, NiOOH on the surface of the first lithium-nickel composite oxide reacted with the excessive Li to be converted to a second lithium-nickel composite oxide including a domain having the NaCl-type crystal structure. As a result, active material particles having a surface layer portion including element M and a second lithium-nickel composite oxide was obtained.

Presence of the second lithium-nickel composite oxide (a domain having the NaCl-type crystal structure) was confirmed by electron diffraction measurement. In Examples below as well, presence of the domain having the NaCl-type crystal structure in the active material particles was confirmed by electron diffraction measurement.

In the Case of Comparative Example Battery m13

Active material particles were synthesized in the same manner as Comparative Example Battery a36 in Example 1, except that a first lithium-nickel composite oxide including excessive lithium (Li_(1.03)Ni_(0.8)Co_(0.15)Al_(0.05)O₂) was used.

In the Case of Comparative Example Battery m14

Active material particles were synthesized in the same manner as Comparative Example Battery a37 of Example 1, except that a first lithium-nickel composite oxide including excessive lithium (Li_(1.03)Ni_(0.8)Co_(0.15)Al_(0.05)O₂) was used. That is, Li_(1.03)Ni_(0.8)Co_(0.15)Al_(0.05)O₂ as is was used as the positive electrode active material.

TABLE 13 First Lithium-Nickel Composite Oxide: Li_(1.03)Ni_(0.80)Co_(0.15)Al_(0.05)O₂ Internal Short Circuit Safety 60° C.- Environment Discharge Crush Speed to be Performance 5 mm/Sec Allowed to Stand Discharge Highest Amount NaCl-type Crystal Temperature · Baking 400 mA 4000 mA Temperature Battery Added Structure Humidity Atmosphere- at 0° C. at 0° C. Reached No Element M (mol %) Domain (° C. · %) Temperature (mAh) (mAh) (° C.) Ex. M1 Ta 0.5 Present 25 · 55 Oxygen-650° C. 1982 1901 71 Ex. M2 2.0 1984 1902 76 Ex. M3 Al 0.5 1980 1902 72 Ex. M4 2.0 1989 1904 70 Ex. M5 Zr 0.5 1988 1908 68 Ex. M6 2.0 1987 1908 62 Ex. M7 Mg 0.5 1992 1909 71 Ex. M8 2.0 1991 1910 72 Ex. M9 In 0.5 1991 1912 71 Ex. M10 2.0 1992 1915 66 Ex. M11 Sn 0.5 1992 1910 70 Ex. M12 2.0 1991 1908 70 Ex. M13 Mn 0.5 1988 1902 68 Ex. M14 2.0 1990 1901 75 Ex. M15 B 0.5 1992 1902 71 Ex. M16 2.0 1994 1902 74 Ex. M17 W 0.5 1992 1901 72 Ex. M18 2.0 1990 1905 72 Ex. M19 Nb 0.5 1982 1904 71 Ex. M20 2.0 1988 1902 70 Ex. M21 Mo 0.5 1991 1904 66 Ex. M22 2.0 1991 1906 71 Ex. M23 Ta 2.5 1992 1800 75 Ex. M24 Al 1990 1802 77 Ex. M25 Zr 1988 1801 74 Ex. M26 Mg 1981 1800 72 Ex. M27 In 1984 1802 71 Ex. M28 Sn 1988 1800 65 Ex. M29 Mn 1989 1804 69 Ex. M30 B 1990 1805 72 Ex. M31 W 1991 1805 69 Ex. M32 Nb 1992 1804 72 Ex. M33 Mo 1992 1810 71 Ex. M34 Ta 0.5 60 · 55 1801 1700 71 Ex. M35 Al 1800 1689 70 Ex. M36 Zr 1805 1700 69 Ex. M37 Mg 1815 1710 69 Ex. M38 In 1802 1712 69 Ex. M39 Sn 1800 1715 71 Ex. M40 Mn 1804 1700 70 Ex. M41 B 1804 1702 72 Ex. M42 W 1805 1699 68 Ex. M43 Nb 1806 1698 69 Ex. M44 Mo 1805 1700 68 Comp. Ex. m1 Ta 0.5 Absent 25 · 20 1991 1915 118 Comp. Ex. m2 Al 1992 1910 119 Comp. Ex. m3 Zr 1988 1915 121 Comp. Ex. m4 Mg 1991 1912 115 Comp. Ex. m5 In 1992 1900 116 Comp. Ex. m6 Sn 1988 1911 121 Comp. Ex. m7 Mn 1989 1907 120 Comp. Ex. m8 B 1989 1905 125 Comp. Ex. m9 W 1990 1901 124 Comp. Ex. m10 Nb 1990 1900 118 Comp. Ex. m11 Mo 1995 1900 119 Comp. Ex. m12 Absent — Present 25 · 55 1750 1600 70 Comp. Ex. m13 Absent Mixed Gas of 2002 1900 120 Nitrogen:Hydrogen = 95:5 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. m14 Not Carried Out 2004 1910 125

The evaluation results are shown below.

In Example Batteries M1 to M22, in which the surface layer portion includes element M and the second lithium-nickel composite oxide, and in which the amount of element M relative to the first lithium-nickel composite oxide is 0.5 mol % or 2 mol %, the heat generation was quite small in the crush test. In these batteries, the discharge capacity with 2 CmA discharge at 0° C. is the same level as that of Comparative Example Battery m14, in which the first lithium-nickel composite oxide was used as is.

In Example Batteries M23 to M33, in which the amount of element M relative to the first lithium-nickel composite oxide was 2.5 mol %, the discharge capacity with 2 CmA discharge at 0° C. declined. Probably due to the compound of element M included in the surface layer portion and the second lithium-nickel composite oxide not being electrochemically active, it became resistance.

In Example Batteries M34 to M44, in which a condition for allowing the first lithium-nickel composite oxide carrying element M before baking to stand was changed to give high temperature, the discharge capacity tended to become low. This is probably because the portion other than the side reaction active points of the first lithium-nickel composite oxide was converted to a domain having the NaCl-type crystal structure.

In Comparative Example Battery m12, in which the first lithium-nickel composite oxide baked after being allowed to stand without carrying element M at a temperature of 25° C. and a humidity of 55% for 24 hours, the discharge capacity was not sufficient. This is probably because absence of element M at the surface thereof caused the first lithium-nickel composite oxide to deteriorate.

In Comparative Example Batteries m1 to 11, in which a condition for allowing the first lithium-nickel composite oxide carrying element M before baking to stand was changed to give low humidity, a large degree of heat generation was caused in the crush test. This is probably because the domain having the NaCl-type crystal structure which inactivate the side reaction active points of the first lithium-nickel composite oxide was not produced.

In Comparative Example Battery m13, in which the positive electrode active material with the reduced layer formed on the first lithium-nickel composite oxide surface, the discharge capacity with 2 CmA (4000 mAh) discharge at 0° C. was not sufficient. This is probably because the first lithium-nickel composite oxide surface is covered with Ni or Co having low oxidation number and electrochemical activity.

The results above were the same as the case when the surface layer portion includes element M and Ni_(1-δ)O (0≦δ≦0.1).

EXAMPLE 12

A first lithium-nickel composite oxide having a composition of Li_(1.03)Ni_(0.9)Co_(0.07)Al_(0.03)O₂ was obtained by using nickel sulfate, cobalt sulfate, and aluminum sulfate so that a molar ratio of Ni atoms, Co atoms, and Al atoms was 90:7:3 upon synthesizing the first lithium composite oxide. Example Batteries N1 to N44 and Comparative Example Batteries n1 to n14 were made in the same manner as Example Batteries M1 to M44 and Comparative Example Batteries m1 to m14, respectively, except that this first lithium-nickel composite oxide was used as the raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Table 14.

TABLE 14 First Lithium-Nickel Composite Oxide: Li_(1.03)Ni_(0.90)Co_(0.07)Al_(0.03)O₂ Internal Short Circuit Safety 60° C.- Environment Discharge Crush Speed to be Performance 5 mm/Sec Allowed to Stand Discharge Highest Amount NaCl-type Crystal Temperature · Baking 400 mA 4000 mA Temperature Battery Added Structure Humidity Atmosphere- at 0° C. at 0° C. Reached No Element M (mol %) Domain (° C. · %) Temperature (mAh) (mAh) (° C.) Ex. N1 Ta 0.5 Present 25 · 55 Oxygen-650° C. 1995 1901 74 EX. N2 2.0 1997 1902 75 Ex. N3 Al 0.5 1992 1910 65 Ex. N4 2.0 1995 1901 72 Ex. N5 Zr 0.5 1989 1904 65 Ex. N6 2.0 1994 1904 71 Ex. N7 Mg 0.5 1989 1902 70 Ex. N8 2.0 1992 1905 72 Ex. N9 In 0.5 1994 1900 68 Ex. N10 2.0 1995 1900 69 Ex. N11 Sn 0.5 1992 1902 68 Ex. N12 2.0 1990 1905 70 Ex. N13 Mn 0.5 1990 1904 70 Ex. N14 2.0 1992 1910 69 Ex. N15 B 0.5 1990 1905 68 Ex. N16 2.0 1990 1902 62 Ex. N17 W 0.5 1995 1904 68 Ex. N18 2.0 1989 1902 69 Ex. N19 Nb 0.5 1989 1906 66 Ex. N20 2.0 1992 1904 65 Ex. N21 Mo 0.5 1991 1900 68 Ex. N22 2.0 1990 1902 69 Ex. N23 Ta 2.5 1990 1805 67 Ex. N24 Al 1990 1800 69 Ex. N25 Zr 1994 1802 68 Ex. N26 Mg 1992 1801 69 Ex. N27 In 1991 1802 70 Ex. N28 Sn 1992 1805 71 Ex. N29 Mn 1995 1800 65 Ex. N30 B 1994 1804 68 Ex. N31 W 1988 1802 69 Ex. N32 Nb 1989 1800 70 Ex. N33 Mo 1982 1800 70 Ex. N34 Ta 0.5 60 · 55 1800 1700 70 Ex. N35 Al 1802 1701 69 Ex. N36 Zr 1800 1705 68 Ex. N37 Mg 1801 1704 67 Ex. N38 In 1802 1704 68 Ex. N39 Sn 1805 1706 70 Ex. N40 Mn 1804 1702 69 Ex. N41 B 1805 1704 71 Ex. N42 W 1804 1704 69 Ex. N43 Nb 1805 1710 68 Ex. N44 Mo 1810 1700 67 Comp. Ex. n1 Ta 0.5 Absent 25 · 20 1992 1912 120 Comp. Ex. n2 Al 1990 1910 118 Comp. Ex. n3 Zr 1990 1914 120 Comp. Ex. n4 Mg 1995 1915 118 Comp. Ex. n5 In 1994 1915 119 Comp. Ex. n6 Sn 1990 1910 119 Comp. Ex. n7 Mn 1991 1910 121 Comp. Ex. n8 B 1989 1911 122 Comp. Ex. n9 W 1988 1912 122 Comp. Ex. n10 Nb 1991 1911 117 Comp. Ex. n11 Mo 1994 1915 120 Comp. Ex. n12 Not — Present 25 · 55 1720 1599 65 Comp. Ex. n13 Added Absent Mixed Gas of 2005 1901 122 Nitrogen: Hydregen = 95:5 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. n14 Not Carried Out 2007 1905 127

EXAMPLE 13

A first lithium-nickel composite oxide having a composition of Li_(1.03)Ni_(0.25)Co_(0.25)Al_(0.50)O₂ was obtained by using nickel sulfate, cobalt sulfate, and aluminum sulfate so that a molar ratio of Ni atoms, Co atoms, and Al atoms was 25:25:50 upon synthesizing the first lithium-nickel composite oxide. Example Batteries O1 to O44 and Comparative Example Batteries o1 to o14 were made in the same manner as Example Batteries M1 to M44 and Comparative Example Batteries m1 to m14, respectively, except that this first lithium-nickel composite oxide was used as the raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Table 15.

TABLE 15 First Lithium-Nickel Composite Oxide: Li_(1.03)Ni_(0.25)Co_(0.25)Al_(0.50)O₂ Internal Short Circuit Safety 60° C.- Environment Discharge Crush Speed to be Performance 5 mm/Sec Allowed to Stand Discharge Highest Amount NaCl-type Crystal Temperature · Baking 400 mA 4000 mA Temperature Battery Added Structure Humidity Atmosphere- at 0° C. at 0° C. Reached No Element M (mol %) Domain (° C. · %) Temperature (mAh) (mAh) (° C.) Ex. O1 Ta 0.5 Present 25 · 55 Oxygen- 1482 1450 64 Ex. O2 2.0 650° C. 1488 1452 67 Ex. O3 Al 0.5 1481 1452 62 Ex. O4 2.0 1480 1455 64 Ex. O5 Zr 0.5 1471 1455 62 Ex. O6 2.0 1475 1460 66 Ex. O7 Mg 0.5 1474 1458 69 Ex. O8 2.0 1472 1458 68 Ex. O9 In 0.5 1477 1457 64 Ex. O10 2.0 1480 1458 69 Ex. O11 Sn 0.5 1474 1455 75 Ex. O12 2.0 1477 1450 69 Ex. O13 Mn 0.5 1481 1456 64 Ex. O14 2.0 1480 1452 75 Ex. O15 B 0.5 1488 1453 66 Ex. O16 2.0 1477 1455 68 Ex. O17 W 0.5 1478 1455 71 Ex. O18 2.0 1482 1458 70 Ex. O19 Nb 0.5 1488 1455 65 Ex. O20 2.0 1487 1458 70 Ex. O21 Mo 0.5 1485 1455 72 Ex. O22 2.0 1477 1459 67 Ex. O23 Ta 2.5 1478 1350 70 Ex. O24 Al 1485 1352 70 Ex. O25 Zr 1488 1355 61 Ex. O26 Mg 1482 1354 65 Ex. O27 In 1472 1352 75 Ex. O28 Sn 1482 1350 60 Ex. O29 Mn 1488 1350 69 Ex. O30 B 1488 1351 68 Ex. O31 W 1482 1352 68 Ex. O32 Nb 1485 1355 70 Ex. O33 Mo 1482 1355 70 Ex. O34 Ta 0.5 60 · 55 1355 1201 59 Ex. O35 Al 1352 1199 62 Ex. O36 Zr 1351 1198 70 Ex. O37 Mg 1355 1197 66 Ex. O38 In 1352 1199 68 Ex. O39 Sn 1354 1197 68 Ex. O40 Mn 1356 1200 70 Ex. O41 B 1355 1201 70 Ex. O42 W 1350 1205 65 Ex. O43 Nb 1350 1202 72 Ex. O44 Mo 1352 1200 69 Comp. Ex. o1 Ta 0.5 Absent 25 · 20 1492 1420 115 Comp. Ex. o2 Al 1490 1420 120 Comp. Ex. o3 Zr 1498 1422 112 Comp. Ex. o4 Mg 1497 1425 100 Comp. Ex. o5 In 1485 1420 120 Comp. Ex. o6 Sn 1477 1420 115 Comp. Ex. o7 Mn 1488 1420 120 Comp. Ex. o8 B 1487 1420 115 Comp. Ex. o9 W 1496 1420 122 Comp. Ex. o10 Nb 1479 1422 124 Comp. Ex. o11 Mo 1477 1425 105 Comp. Ex. o12 Not — Present 25 · 55 1320 1170 80 Comp. Ex. o13 Added Absent Mixed Gas of 1500 1400 120 Nitrogen:Hydrogen = 95:5 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. o14 Not Carried Out 1500 1420 125

EXAMPLE 14

A first lithium-nickel composite oxide having a composition of Li_(1.03)Ni_(0.25)Cu_(0.50)Al_(0.25)O₂ was obtained by using nickel sulfate, cobalt sulfate, and aluminum sulfate so that a molar ratio of Ni atoms, Co atoms, and Al atoms was 25:50:25 upon synthesizing the first lithium-nickel composite oxide. Example Batteries P1 to P44 and Comparative Example Batteries p1 to p14 were made in the same manner as Example Batteries M1 to M44 and Comparative Example Batteries m1 to m14, respectively, except that this first lithium-nickel composite oxide was used as the raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Table 16.

TABLE 16 First Lithium-Nickel Composite Oxide: Li_(1.03)Ni_(0.25)Co_(0.50)Al_(0.25)O₂ Internal Short Circuit Safety 60° C.- Environment Discharge Crush Speed to be Allowed Performance 5 mm/Sec NaCl-type to Stand Discharge Highest Amount Crystal Temperature · Baking 400 mA 4000 mA Temperature Battery Added Structure Humidity Atmosphere- at 0° C. at 0° C. Reached No Element M (mol %) Domain (° C. · %) Temperature (mAh) (mAh) (° C.) Ex. P1 Ta 0.5 Present 25 · 55 Oxygen-650° C. 1882 1812 70 Ex. P2 2.0 1891 1815 62 Ex. P3 Al 0.5 1880 1810 65 Ex. P4 2.0 1882 1815 70 Ex. P5 Zr 0.5 1880 1812 71 Ex. P6 2.0 1881 1810 71 Ex. P7 Mg 0.5 1890 1812 65 Ex. P8 2.0 1890 1815 65 Ex. P9 In 0.5 1879 1810 71 Ex. P10 2.0 1888 1812 70 Ex. P11 Sn 0.5 1890 1814 61 Ex. P12 2.0 1887 1816 70 Ex. P13 Mn 0.5 1885 1815 65 Ex. P14 2.0 1884 1815 65 Ex. P15 B 0.5 1888 1815 71 Ex. P16 2.0 1889 1810 72 Ex. P17 W 0.5 1890 1811 64 Ex. P18 2.0 1890 1812 68 Ex. P19 Nb 0.5 1870 1815 62 Ex. P20 2.0 1885 1812 62 Ex. P21 Mo 0.5 1889 1800 72 Ex. P22 2.0 1885 1800 72 Ex. P23 Ta 2.5 1891 1601 70 Ex. P24 Al 1880 1605 72 Ex. P25 Zr 1879 1602 67 Ex. P26 Mg 1892 1608 68 Ex. P27 In 1891 1607 64 Ex. P28 Sn 1889 1602 65 Ex. P29 Mn 1895 1603 69 Ex. P30 B 1897 1608 65 Ex. P31 W 1889 1600 68 Ex. P32 Nb 1890 1601 65 Ex. P33 Mo 1890 1602 60 Ex. P34 Ta 0.5 60 · 55 1602 1502 67 Ex. P35 Al 1604 1500 65 Ex. P36 Zr 1605 1504 70 Ex. P37 Mg 1610 1501 65 Ex. P38 In 1605 1508 65 Ex. P39 Sn 1608 1509 70 Ex. P40 Mn 1604 1510 64 Ex. P41 B 1610 1511 70 Ex. P42 W 1609 1512 68 Ex. P43 Nb 1608 1513 70 Ex. P44 Mo 1608 1512 72 Comp. Ex. p1 Ta 0.5 Absent 25 · 20 1882 1810 122 Comp. Ex. p2 Al 1884 1809 123 Comp. Ex. p3 Zr 1880 1804 124 Comp. Ex. p4 Mg 1891 1809 121 Comp. Ex. p5 In 1890 1802 122 Comp. Ex. p6 Sn 1888 1809 125 Comp. Ex. p7 Mn 1879 1807 122 Comp. Ex. p8 B 1880 1807 124 Comp. Ex. p9 W 1889 1809 122 Comp. Ex. p10 Nb 1880 1087 120 Comp. Ex. p11 Mo 1890 1807 120 Comp. Ex. p12 Not — Present 25 · 55 1608 1479 79 Comp. Ex. p13 Added Absent Mixed Gas of 1890 1820 130 Nitrngen:Hydrogen = 95:5 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. p14 Not Carried Out 1895 1827 132

EXAMPLE 15

A first lithium-nickel composite oxide having a composition of Li_(1.03)Ni_(0.90)Co_(0.10)O₂ was obtained by using nickel sulfate and cobalt sulfate without using aluminum sulfate so that a molar ratio of Ni atoms to Co atoms was 90:10 upon synthesizing the first lithium-nickel composite oxide. Example Batteries Q1 to Q44 and Comparative Example Batteries q1 to q14 were made in the same manner as Example Batteries M1 to M44 and Comparative Example Batteries m1 to m14, respectively, except that this first lithium-nickel composite oxide was used as the raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Table 17.

TABLE 17 First Lithium-Nickel Composite Oxide: Li_(1.03)Ni_(0.90)Co_(0.10)O₂ Internal Short Circuit Safety 60° C.- Environment to Discharge Crush Speed be Allowed to Performance 5 mm/Sec NaCl-type Stand Discharge Highest Amount Crystal Temperature · Baking 400 mA 4000 mA Temperature Battery Added Structure Humidity Atmosphere- at 0° C. at 0° C. Reached No Element M (mol %) Domain (° C. · %) Temperature (mAh) (mAh) (° C.) Ex. Q1 Ta 0.5 Present 25 · 55 Oxygen-650° C. 2001 1901 70 Ex. Q2 2.0 2002 1902 75 Ex. Q3 Al 0.5 2003 1907 62 Ex. Q4 2.0 2004 1905 67 Ex. Q5 Zr 0.5 2001 1901 64 Ex. Q6 2.0 2005 1905 72 Ex. Q7 Mg 0.5 2008 1907 62 Ex. Q8 2.0 2007 1901 67 Ex. Q9 In 0.5 2000 1900 68 Ex. Q10 2.0 2001 1902 62 Ex. Q11 Sn 0.5 2006 1908 62 Ex. Q12 2.0 2007 1908 60 Ex. Q13 Mn 0.5 2009 1901 62 Ex. Q14 2.0 2005 1904 65 Ex. Q15 B 0.5 2004 1903 70 Ex. Q16 2.0 2000 1905 60 Ex. Q17 W 0.5 2003 1908 68 Ex. Q18 2.0 2000 1907 65 Ex. Q19 Nb 0.5 2004 1902 62 Ex. Q20 2.0 2005 1900 65 Ex. Q21 Mo 0.5 2002 1901 67 Ex. Q22 2.0 2004 1908 65 Ex. Q23 Ta 2.5 2002 1701 70 Ex. Q24 Al 2004 1701 70 Ex. Q25 Zr 2001 1705 65 Ex. Q26 Mg 2000 1706 70 Ex. Q27 In 2004 1707 67 Ex. Q28 Sn 2003 1701 65 Ex. Q29 Mn 2002 1704 71 Ex. Q30 B 2002 1707 68 Ex. Q31 W 2004 1700 65 Ex. Q32 Nb 2001 1705 71 Ex. Q33 Mo 2003 1704 65 Ex. Q34 Ta 0.5 60 · 55 1750 1611 60 Ex. Q35 Al 1740 1613 72 Ex. Q36 Zr 1747 1609 75 Ex. Q37 Mg 1757 1619 62 Ex. Q38 In 1758 1620 70 Ex. Q39 Sn 1760 1627 62 Ex. Q40 Mn 1747 1622 67 Ex. Q41 B 1749 1619 68 Ex. Q42 W 1752 1617 69 Ex. Q43 Nb 1755 1617 64 Ex. Q44 Mo 1754 1627 64 Comp. Ex. q1 Ta 0.5 Absent 25 · 20 2003 1901 117 Comp. Ex. q2 Al 2005 1902 117 Comp. Ex. q3 Zr 2004 1909 119 Comp. Ex. q4 Mg 2005 1904 117 Comp. Ex. q5 In 2000 1902 115 Comp. Ex. q6 Sn 2003 1907 114 Comp. Ex. q7 Mn 2005 1903 119 Comp. Ex. q8 B 2002 1901 119 Comp. Ex. q9 W 2004 1900 118 Comp. Ex. q10 Nb 2003 1904 118 Comp. Ex. q11 Mo 2007 1900 118 Comp. Ex. q12 Not — Present 25 · 55 1760 1611 70 Comp. Ex. q13 Added Absent Mixed Gas of 2008 1910 112 Nitrogen:Hydrogen = 95:5 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. q14 Not Carried Out 2007 1919 122

EXAMPLE 16

A first lithium-nickel composite oxide having a composition of Li_(1.03)Ni_(0.50)Co_(0.50)O₂ was obtained by using nickel sulfate and cobalt sulfate without using aluminum sulfate so that a molar ratio of Ni atoms to Co atoms was 50:50 upon synthesizing the first lithium-nickel composite oxide. Example Batteries R1 to R44 and Comparative Example Batteries r1 to r14 were made in the same manner as Example Batteries M1 to M44 and Comparative Example Batteries m1 to m14, respectively, except that this first lithium-nickel composite oxide was used as the raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Table 18.

TABLE 18 First Lithium-Nickel Composite Oxide: Li_(1.03)Ni_(0.50)Co_(0.50)O₂ Internal Short Circuit Safety 60° C.- Environment to Discharge Crush Speed be Allowed to Performance 5 mm/Sec Stand Discharge Highest Amount NaCl-type Crystal Temperature · Baking 400 mA 4000 mA Temperature Battery Added Structure Humidity Atmosphere- at 0° C. at 0° C. Reached No Element M (mol %) Domain (° C. · %) Temperature (mAh) (mAh) (° C.) Ex. R1 Ta 0.5 Present 25 · 55 Oxygen- 2001 1901 64 Ex. R2 2.0 650° C. 2002 1903 68 Ex. R3 Al 05 2003 1902 65 Ex. R4 2.0 2002 1900 62 Ex. R5 Zr 0.5 2004 1904 61 Ex. R6 2.0 2005 1905 67 Ex. R7 Mg 0.5 2000 1902 65 Ex. R8 2.0 2000 1907 65 Ex. R9 In 0.5 2001 1908 61 Ex. R10 2.0 2001 1907 62 Ex. R11 Sn 0.5 2002 1905 62 Ex. R12 2.0 2004 1906 66 Ex. R13 Mn 0.5 2003 1907 66 Ex. R14 2.0 2005 1905 65 Ex. R15 B 0.5 2001 1906 70 Ex. R16 2.0 2000 1907 64 Ex. R17 W 0.5 2001 1907 66 Ex. R18 2.0 2004 1917 62 Ex. R19 Nb 0.5 2005 1907 64 Ex. R20 2.0 2006 1905 64 Ex. R21 Mo 0.5 2003 1907 67 Ex. R22 2.0 2001 1900 60 Ex. R23 Ta 2.5 2004 1701 65 Ex. R24 Al 2001 1702 64 Ex. R25 Zr 2000 1708 65 Ex. R26 Mg 2002 1709 65 Ex. R27 In 2000 1706 65 Ex. R28 Sn 2001 1704 65 Ex. R29 Mn 2003 1702 62 Ex. R30 B 2004 1700 65 Ex. R31 W 2002 1703 63 Ex. R32 Nb 2001 1702 66 Ex. R33 Mo 2005 1708 65 Ex. R34 Ta 0.5 60 · 55 1770 1637 62 Ex. R35 Al 1777 1647 65 Ex. R36 Zr 1780 1644 62 Ex. R37 Mg 1782 1650 65 Ex. R38 In 1772 1638 67 Ex. R39 Sn 1773 1637 68 Ex. R40 Mn 1774 1657 65 Ex. R41 B 1773 1652 65 Ex. R42 W 1772 1650 64 Ex. R43 Nb 1777 1677 61 Ex. R44 Mo 1771 1667 69 Comp. Ex. r1 Ta 0.5 Absent 25 · 20 2002 1902 119 Comp. Ex. r2 Al 2000 1900 111 Comp. Ex. r3 Zr 2003 1905 110 Comp. Ex. r4 Mg 2001 1905 113 Comp. Ex. r5 In 2000 1900 116 Comp. Ex. r6 Sn 2001 1906 115 Comp. Ex. r7 Mn 2002 1907 110 Comp. Ex. r8 B 2006 1901 119 Comp. Ex. r9 W 2008 1903 121 Comp. Ex. r10 Nb 2007 1907 122 Comp. Ex. r11 Mo 2005 1900 111 Comp. Ex. r12 Not — Present 25 · 55 1711 1655 65 Comp. Ex. r13 Added Absent Mixed Gas of 2009 1920 130 Nitrogen:Hydrogen = 95:5 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. r14 Not Carried Out 2010 1927 137

EXAMPLE 17

Nickel sulfate, cobalt sulfate, and aluminum sulfate were mixed so that a molar ratio of Ni atoms, Co atoms, and Al atoms was 80:15:3. The obtained mixture in an amount of 3.2 kg was dissolved in 10 L of water, to obtain a raw material solution. To the raw material solution, 400 g of sodium hydroxide was added to form a precipitate. The precipitate was sufficiently washed with water and dried, to obtain a coprecipitated hydroxide.

To 3 kg of the obtained coprecipitated hydroxide of Ni—Co—Al, 870 g of lithium hydroxide and 378 g of manganese nitrate were mixed. The obtained mixture was baked under an atmosphere with an oxygen partial pressure of 0.5 atm at a synthesizing temperature of 750° C. for 10 hours, to obtain a first lithium-nickel composite oxide including excessive lithium (composition: Li_(1.03)Ni_(0.8)Co_(0.15)Al_(0.03)Mn_(0.02)O₂).

Example Batteries S1 to S44 and Comparative Example Batteries s1 to s14 were made in the same manner as Example Batteries M1 to M44 and Comparative Example Batteries m1 to m14, respectively, except that the lithium composite oxide was used as a raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Table 19.

TABLE 19 First Lithium-Nickel Composite Oxide: Li_(1.03)Ni_(0.80)Co_(0.15)Al_(0.03)Mn_(0.02)O₂ Internal Short Circuit Safety 60° C. - Crush Environment Discharge Speed to be Allowed Performance 5 mm/Sec NaCl-type to Stand Discharge Highest Amount Crystal Temperature · Baking 400 mA 4000 mA Temperature Battery Added Structure Humidity Atmosphere · at 0° C. at 0° C. Reached No Element M (mol %) Domain (° C. · %) Temperature (mAh) (mAh) (° C.) Ex. S1 Ta 0.5 Present 25 · 55 Oxygen- 2004 1902 66 Ex. S2 2.0 650° C. 2005 1900 67 Ex. S3 Al 0.5 2004 1904 65 Ex. S4 2.0 2005 1907 60 Ex. S5 Zr 0.5 2002 1905 65 Ex. S6 2.0 2005 1902 62 Ex. S7 Mg 0.5 2008 1904 60 Ex. S8 2.0 2009 1907 64 Ex. S9 In 0.5 2007 1907 65 Ex. S10 2.0 2007 1901 61 Ex. S11 Sn 0.5 2006 1905 65 Ex. S12 2.0 2004 1907 65 Ex. S13 Mn 0.5 2005 1901 64 Ex. S14 2.0 2004 1900 64 Ex. S15 B 0.5 2005 1905 64 Ex. S16 2.0 2003 1907 67 Ex. S17 W 0.5 2002 1908 66 Ex. S18 2.0 2005 1909 60 Ex. S19 Nb 0.5 2002 1910 61 Ex. S20 2.0 2000 1901 67 Ex. S21 Mo 0.5 2005 1912 68 Ex. S22 2.0 2005 1900 65 Ex. S23 Ta 2.5 2004 1711 62 Ex. S24 Al 2000 1720 60 Ex. S25 Zr 2001 1727 62 Ex. S26 Mg 2002 1722 68 Ex. S27 In 2002 1715 68 Ex. S28 Sn 2008 1720 64 Ex. S29 Mn 2002 1710 66 Ex. S30 B 2002 1715 64 Ex. S31 W 2000 1726 60 Ex. S32 Nb 2005 1717 64 Ex. S33 Mo 2004 1709 66 Ex. S34 Ta 0.5 60 · 55 1755 1667 68 Ex. S35 Al 1757 1670 66 Ex. S36 Zr 1767 1671 65 Ex. S37 Mg 1754 1669 62 Ex. S38 In 1752 1670 62 Ex. S39 Sn 1747 1657 64 Ex. S40 Mn 1767 1671 65 Ex. S41 B 1765 1682 65 Ex. S42 W 1774 1682 65 Ex. S43 Nb 1777 1677 62 Ex. S44 Mo 1787 1680 66 Comp. Ex. s1 Ta 0.5 Absent 25 · 20 2001 1907 122 Comp. Ex. s2 Al 2003 1910 120 Comp. Ex. s3 Zr 2002 1911 121 Comp. Ex. s4 Mg 2005 1912 118 Comp. Ex. s5 In 2001 1908 119 Comp. Ex. s6 Sn 2003 1909 117 Comp. Ex. s7 Mn 2005 1907 119 Comp. Ex. s8 B 2007 1910 121 Comp. Ex. s9 W 2002 1911 119 Comp. Ex. s10 Nb 2003 1908 120 Comp. Ex. s11 Mo 2005 1907 118 Comp. Ex. s12 Not — Present 25 · 55 1734 1620 66 Comp. Ex. s13 Added Absent Mixed Gas of 2009 1919 122 Nitrogen:Hydrogen = 95:5 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. s14 Not Carried Out 2010 1927 132

EXAMPLE 18

To 3 kg of a coprecipitated hydroxide of Ni—Co—Al prepared in the same manner as Example 17, 870 g of lithium hydroxide and 378 g of magnesium sulfate were mixed. The obtained mixture was baked under an atmosphere with an oxygen partial pressure of 0.5 atm at a synthesizing temperature of 750° C. for 10 hours, to obtain a first lithium-nickel composite oxide including excessive lithium (composition: Li_(1.03)Ni_(0.8)Co_(0.15)Al_(0.03)Mg_(0.02)O₂).

Example Batteries T1 to T44 and Comparative Example Batteries t1 to t14 were made in the same manner as Example Batteries M1 to M44 and Comparative Example Batteries m1 to m14, respectively, except that this lithium composite oxide was used as a raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Table 20.

TABLE 20 First Lithium-Nickel Composite Oxide: Li_(1.03)Ni_(0.80)Co_(0.15)Al_(0.03)Mg_(0.02)O₂ Internal Short Circuit Safety 60° C. - Crush Environment Discharge Speed to be Allowed Performance 5 mm/Sec NaCl-type to Stand Discharge Highest Amount Crystal Temperature · Baking 400 mA 4000 mA Temperature Battery Added Structure Humidity Atmosphere · at 0° C. at 0° C. Reached No Element M (mol %) Domain (° C. · %) Temperature (mAh) (mAh) (° C.) Ex. T1 Ta 0.5 Present 25 · 55 Oxygen · 2002 1902 64 Ex. T2 2.0 650° C. 2004 1900 60 Ex. T3 Al 0.5 2005 1902 66 Ex. T4 2.0 2002 1903 63 Ex. T5 Zr 0.5 2001 1904 62 Ex. T6 2.0 2000 1901 64 Ex. T7 Mg 0.5 2005 1902 62 Ex. T8 2.0 2002 1901 67 Ex. T9 In 0.5 2000 1907 62 Ex. T10 2.0 2005 1905 69 Ex. T11 Sn 0.5 2001 1900 62 Ex. T12 2.0 2002 1900 61 Ex. T13 Mn 0.5 2000 1902 63 Ex. T14 2.0 2004 1902 62 Ex. T15 B 0.5 2004 1905 65 Ex. T16 2.0 2005 1905 66 Ex. T17 W 0.5 2002 1900 67 Ex. T18 2.0 2000 1900 64 Ex. T19 Nb 0.5 2004 1900 65 Ex. T20 2.0 2005 1901 64 Ex. T21 Mo 0.5 2007 1902 62 Ex. T22 2.0 2003 1902 67 Ex. T23 Ta 2.5 2005 1702 62 Ex. T24 Al 2003 1700 67 Ex. T25 Zr 2004 1705 63 Ex. T26 Mg 2005 1703 64 Ex. T27 In 2008 1704 64 Ex. T28 Sn 2009 1705 67 Ex. T29 Mn 2007 1705 63 Ex. T30 B 2007 1707 66 Ex. T31 W 2007 1707 68 Ex. T32 Nb 2006 1700 62 Ex. T33 Mo 2005 1700 62 Ex. T34 Ta 0.5 60 · 55 1782 1611 62 Ex. T35 Al 1777 1614 60 Ex. T36 Zr 1779 1626 61 Ex. T37 Mg 1781 1627 64 Ex. T38 In 1782 1634 62 Ex. T39 Sn 1783 1626 65 Ex. T40 Mn 1787 1620 64 Ex. T41 B 1771 1630 65 Ex. T42 W 1773 1643 63 Ex. T43 Nb 1772 1625 61 Ex. T44 Mo 1777 1632 64 Comp. Ex. t1 Ta 0.5 Absent 25 · 20 2001 1907 120 Comp. Ex. t2 Al 2004 1903 121 Comp. Ex. t3 Zr 2003 1906 120 Comp. Ex. t4 Mg 2004 1909 119 Comp. Ex. t5 In 2005 1900 124 Comp. Ex. t6 Sn 2001 1901 125 Comp. Ex. t7 Mn 2002 1902 130 Comp. Ex. t8 B 2001 1901 128 Comp. Ex. t9 W 2002 1907 122 Comp. Ex. t10 Nb 2000 1904 129 Comp. Ex. t11 Mo 2005 1905 125 Comp. Ex. t12 Not — Present 25 · 55 1722 1602 69 Comp. Ex. t13 Added Absent Mixed Gas of 2007 1907 132 Nitrogen:Hydrogen = 95:5 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. t14 Not Carried Out 2009 1917 135

EXAMPLE 19

To 3 kg of a coprecipitated hydroxide of Ni—Co—Al prepared in the same manner as Example 17, 870 g of lithium hydroxide and 378 g of calcium hydroxide were mixed. The obtained mixture was baked under an atmosphere with an oxygen partial pressure of 0.5 atm at a synthesizing temperature of 750° C. for 10 hours, to obtain a first lithium-nickel composite oxide including excessive lithium (composition: Li_(1.03)Ni_(0.8)Co_(0.15)Al_(0.03)Ca_(0.02)O₂).

Example Batteries U1 to U44 and Comparative Example Batteries u1 to u35 were made in the same manner as Example Batteries M1 to M44 and Comparative Example Batteries m1 to m14, respectively, except that this lithium composite oxide was used as a raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Table 21.

TABLE 21 First Lithium-Nickel Composite Oxide: Li_(1.03)Ni_(0.80)Co_(0.15)Al_(0.03)Ca_(0.02)O₂ Internal Short Circuit Safety 60° C. - Crush Environment Discharge Speed to be Allowed Performance 5 mm/Sec NaCl-type to Stand Discharge Highest Amount Crystal Temperature · Baking 400 mA 4000 mA Temperature Battery Added Structure Humidity Atmosphere · at 0° C. at 0° C. Reached No Element M (mol %) Domain (° C. · %) Temperature (mAh) (mAh) (° C.) Ex. U1 Ta 0.5 Present 25 · 25 Oxygen · 2002 1912 65 Ex. U2 2.0 650° C. 2004 1911 62 Ex. U3 Al 0.5 2005 1910 65 Ex. U4 2.0 2004 1913 65 Ex. U5 Zr 0.5 2002 1914 64 Ex. U6 2.0 2005 1914 64 Ex. U7 Mg 0.5 2006 1915 62 Ex. U8 2.0 2004 1911 68 Ex. U9 In 0.5 2005 1908 69 Ex. U10 2.0 2002 1909 65 Ex. U11 Sn 0.5 2004 1912 60 Ex. U12 2.0 2005 1914 66 Ex. U13 Mn 0.5 2006 1917 67 Ex. U14 2.0 2007 1908 62 Ex. U15 B 0.5 2004 1915 62 Ex. U16 2.0 2002 1917 62 Ex. U17 W 0.5 2006 1911 68 Ex. U18 2.0 2004 1911 64 Ex. U19 Nb 0.5 2003 1914 64 Ex. U20 2.0 2002 1912 68 Ex. U21 Mo 0.5 2001 1913 67 Ex. U22 2.0 2005 1917 64 Ex. U23 Ta 2.5 2004 1712 64 Ex. U24 Al 2000 1712 61 Ex. U25 Zr 2002 1709 68 Ex. U26 Mg 2005 1710 62 Ex. U27 In 2004 1717 65 Ex. U28 Sn 2003 1703 62 Ex. U29 Mn 2005 1704 62 Ex. U30 B 2000 1707 68 Ex. U31 W 2002 1717 68 Ex. U32 Nb 2005 1710 67 Ex. U33 Mo 2007 1717 64 Ex. U34 Ta 0.5 60 · 55 1774 1660 67 Ex. U35 Al 1779 1664 64 Ex. U36 Zr 1757 1670 64 Ex. U37 Mg 1767 1672 67 Ex. U38 In 1771 1667 62 Ex. U39 Sn 1764 1669 62 Ex. U40 Mn 1757 1672 68 Ex. U41 B 1770 1680 64 Ex. U42 W 1761 1672 64 Ex. U43 Nb 1775 1682 65 Ex. U44 Mo 1770 1682 68 Comp. u1 Ta 0.5 Absent 25 · 20 2003 1907 120 Comp. u2 Al 2007 1902 119 Comp. u3 Zr 2005 1903 117 Comp. u4 Mg 2008 1907 122 Comp. u5 In 2002 1909 120 Comp. u6 Sn 2004 1902 117 Comp. u7 Mn 2007 1904 117 Comp. u8 B 2003 1907 121 Comp. u9 W 2005 1903 119 Comp. u10 Nb 2002 1907 124 Comp. u11 Mo 2000 1902 127 Comp. u12 Not — Present 25 · 55 1727 1600 69 Comp. u13 Added Absent Mixed Gas of 2004 1920 119 Nitrogen:Hydroge = 95:5 (molar ratio) treated at 400° C. for 6 hours Comp. u14 Not Carried Out 2007 1914 120

EXAMPLE 20

To 3 kg of the coprecipitated hydroxide of Ni—Co—Al prepared in the same manner as Example 17, 870 g of lithium hydroxide and 378 g of titanium sulfate were mixed. The obtained mixture was baked under an atmosphere with an oxygen partial pressure of 0.5 atm at a synthesizing temperature of 750° C. for 10 hours, to obtain a first lithium-nickel composite oxide including excessive lithium (composition: Li_(1.03)Ni_(0.8)Co_(0.15)Al_(0.03)Ti_(0.02)O₂).

Example Batteries V1 to V44 and Comparative Example Batteries v1 to v14 were made in the same manner as Example Batteries M1 to M44 and Comparative Example Batteries m1 to m14, respectively, except that this lithium composite oxide was used for a raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Table 22.

TABLE 22 First Lithium-Nickel Composite Oxide: Li_(1.03)Ni_(0.80)Co_(0.15)Al_(0.03)Ti_(0.02)O₂ Internal Short Circuit Safety 60° C. - Crush Environment Discharge Speed to be Allowed Performance 5 mm/Sec NaCl-type to Stand Discharge Highest Amount Crystal Temperature · Baking 400 mA 4000 mA Temperature Battery Added Structure Humidity Atmosphere · at 0° C. at 0° C. Reached No Element M (mol %) Domain (° C. · %) Temperature (mAh) (mAh) (° C.) Ex. V1 Ta 0.5 Present 25 · 55 Oxygen · 2002 1902 64 Ex. V2 2.0 650° C. 2002 1900 65 Ex. V3 Al 0.5 2005 1905 67 Ex. V4 2.0 2000 1902 65 Ex. V5 Zr 0.5 2002 1900 64 Ex. V6 2.0 2002 1905 65 Ex. V7 Mg 0.5 2000 1900 68 Ex. V8 2.0 2000 1902 62 Ex. V9 In 0.5 2003 1903 68 Ex. V10 2.0 2004 1903 63 Ex. V11 Sn 0.5 2004 1900 60 Ex. V12 2.0 2002 1903 60 Ex. V13 Mn 0.5 2003 1902 64 Ex. V14 2.0 2003 1905 64 Ex. V15 B 0.5 2005 1903 64 Ex. V16 2.0 2001 1902 61 Ex. V17 W 0.5 2004 1904 62 Ex. V18 2.0 2005 1904 65 Ex. V19 Nb 0.5 2002 1902 68 Ex. V20 2.0 2002 1904 64 Ex. V21 Mo 0.5 2000 1904 68 Ex. V22 2.0 2004 1900 66 Ex. V23 Ta 2.5 2006 1707 60 Ex. V24 Al 2002 1708 62 Ex. V25 Zr 2002 1700 60 Ex. V26 Mg 2003 1704 62 Ex. V27 In 2000 1704 67 Ex. V28 Sn 2006 1707 62 Ex. V29 Mn 2005 1700 62 Ex. V30 B 2002 1710 68 Ex. V31 W 2000 1702 68 Ex. V32 Nb 2006 1700 64 Ex. V33 Mo 2004 1711 64 Ex. V34 Ta 0.5 60 · 55 1175 1627 62 Ex. V35 Al 1777 1622 61 Ex. V36 Zr 1776 1624 65 Ex. V37 Mg 1775 1637 64 Ex. V38 In 1772 1635 60 Ex. V39 Sn 1771 1627 62 Ex. V40 Mn 1772 1647 67 Ex. V41 B 1775 1640 63 Ex. V42 W 1782 1627 62 Ex. V43 Nb 1779 1647 64 Ex. V44 Mo 1778 1617 62 Comp. Ex. v1 Ta 0.5 Absent 25 · 20 2007 1905 119 Comp. Ex. v2 Al 2005 1907 120 Comp. Ex. v3 Zr 2008 1908 124 Comp. Ex. v4 Mg 2004 1902 123 Comp. Ex. v5 In 2008 1907 125 Comp. Ex. v6 Sn 2002 1904 127 Comp. Ex. v7 Mn 2005 1905 121 Comp. Ex. v8 B 2007 1907 127 Comp. Ex. v9 W 2004 1904 124 Comp. Ex. v10 Nb 2002 1907 127 Comp. Ex. v11 Mo 2001 1904 120 Comp. Ex. v12 Not — Present 25 · 55 1720 1609 71 Comp. Ex. v13 Added Absent Mixed Gas of 2009 1912 125 Nitrogen:Hydrogen = 95:5 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. v14 Not Carried Out 2010 1920 127

The results in Tables 14 to 22 showed similar tendency with the case in Example 11.

COMPARATIVE EXAMPLE 3

A first lithium-nickel composite oxide having a composition of Li_(1.03)Ni_(0.20)Co_(0.50)Al_(0.30)O₂ was obtained by using nickel sulfate, cobalt sulfate, and aluminum sulfate so that a molar ratio of Ni atoms, Co atoms, and Al atoms was 20:50:30 upon synthesizing the lithium composite oxide. Comparative Example Batteries w1 to w58 were made in the same manner as Example Batteries M1 to M44 and Comparative Example Batteries m1 to m14, respectively, except that this first lithium-nickel composite oxide was used as the raw material for the active material particles, and the evaluation was carried out in the same manner as Example 1. The results are shown in Table 23.

TABLE 23 First Lithium-Nickel Composite Oxide: Li_(1.03)Ni_(0.20)Co_(0.50)Al_(0.30)O₂ Internal Short Circuit Safety 60° C. - Crush Environment Discharge Speed to be Allowed Performance 5 mm/Sec NaCl-type to Stand Discharge Highest Amount Crystal Temperature · Baking 400 mA 4000 mA Temperature Battery Added Structure Humidity Atmosphere · at 0° C. at 0° C. Reached No Element M (mol %) Domain (° C. · %) Temperature (mAh) (mAh) (° C.) Comp. w1 Ta 0.5 Present 25 · 55 Oxygen · 1810 1710 117 Comp. w2 2.0 650° C. 1815 1710 118 Comp. w3 Al 0.5 1805 1715 115 Comp. w4 2.0 1810 1709 100 Comp. w5 Zr 0.5 1800 1710 120 Comp. w6 2.0 1802 1710 110 Comp. w7 Mg 0.5 1807 1715 106 Comp. w8 2.0 1804 1712 112 Comp. w9 In 0.5 1810 1715 110 Comp. w10 2.0 1800 1705 110 Comp. w11 Sn 0.5 1805 1715 100 Comp. w12 2.0 1810 1710 115 Comp. w13 Mn 0.5 1806 1712 120 Comp. w14 2.0 1810 1720 100 Comp. w15 B 0.5 1805 1708 115 Comp. w16 2.0 1802 1710 118 Comp. w17 W 0.5 1804 1715 117 Comp. w18 2.0 1805 1700 120 Comp. w19 Nb 0.5 1800 1712 120 Comp. w20 2.0 1805 1715 115 Comp. w21 Mo 0.5 1805 1715 115 Comp. w22 2.0 1805 1710 116 Comp. w23 Ta 2.5 1789 1530 125 Comp. w24 Al 1788 1535 115 Comp. w25 Zr 1785 1540 120 Comp. w26 Mg 1779 1530 120 Comp. w27 In 1783 1540 118 Comp. w28 Sn 1785 1530 110 Comp. w29 Mn 1788 1532 115 Comp. w30 B 1782 1535 117 Comp. w31 W 1779 1530 115 Comp. w32 Nb 1780 1530 112 Comp. w33 Mo 1790 1533 110 Comp. w34 Ta 0.5 60 · 55 1770 1622 105 Comp. w35 Al 1769 1623 120 Comp. w36 Zr 1763 1627 117 Comp. w36 Mg 1767 1622 116 Comp. w38 In 1757 1616 110 Comp. w39 Sn 1760 1627 120 Comp. w40 Mn 1762 1620 118 Comp. w41 B 1767 1618 110 Comp. w42 W 1770 1610 120 Comp. w43 Nb 1758 1610 113 Comp. w44 Mo 1759 1612 105 Comp. w45 Ta 0.5 Absent 25 · 20 1805 1709 120 Comp. w46 Al 1805 1715 120 Comp. w47 Zr 1805 1710 118 Comp. w48 Mg 1805 1710 117 Comp. w49 In 1802 1710 115 Comp. w50 Sn 1801 1712 105 Comp. w51 Mn 1806 1715 117 Comp. w52 B 1802 1715 117 Comp. w53 W 1800 1710 119 Comp. w54 Nb 1805 1715 112 Comp. w55 Mo 1800 1705 122 Comp. w56 Not — Present 25 · 55 1760 1601 112 Comp. w57 Added Absent Mixed Gas of 1803 1712 135 Nitrogen:Hydrogen = 95:5 (molar ratio) treated at 400° C. for 6 hours Comp. w58 Not Carried Out 1800 1720 138

No presence of the domain having the NaCl-type crystal structure was confirmed upon analysis of the active material particles of Comparative Example Batteries w1 to w58. The results of Tables 23A and 23B made clear that a large heat generation is caused in the crush test in the case when y+z exceeds 0.75 in the first lithium-nickel composite oxide represented by the general formula Li_(x)Ni_(1-y-z)Co_(y)Me_(z)O₂, not producing the domain having the NaCl-type crystal structure.

COMPARATIVE EXAMPLE 4

Comparative Example Batteries x1 to x58 were made in the same manner as Example Batteries M1 to M44 and Comparative Example Batteries m1 to m14, respectively, except that Li_(1.03)NiO₂ was used as a raw material for the active material particles instead of the first lithium-nickel composite oxide, and the evaluation was carried out in the same manner as Example 1. The results are shown in Table 24.

TABLE 24 First Lithium-Nickel Composite Oxide: Li_(1.03)NiO₂ Internal Short Circuit Safety 60° C. - Crush Environment Discharge Speed to be Allowed Performance 5 mm/Sec NaCl-type to Stand Discharge Highest Amount Crystal Temperature · Baking 400 mA 4000 mA Temperature Battery Added Structure Humidity Atmosphere · at 0° C. at 0° C. Reached No Element M (mol %) Domain (° C. · %) Temperature (mAh) (mAh) (° C.) Comp. Ex. x1 Ta 0.5 Present 25 · 55 Oxygen · 2002 1810 112 Comp. Ex. x2 2.0 650° C. 2004 1811 115 Comp. Ex. x3 Al 0.5 2007 1822 105 Comp. Ex. x4 2.0 2009 1820 117 Comp. Ex. x5 Zr 0.5 2007 1828 117 Comp. Ex. x6 2.0 2005 1819 106 Comp. Ex. x7 Mg 0.5 2004 1811 110 Comp. Ex. x8 2.0 2005 1813 120 Comp. Ex. x9 In 0.5 2008 1810 116 Comp. Ex. x10 2.0 2009 1813 120 Comp. Ex. x11 Sn 0.5 2010 1818 110 Comp. Ex. x12 2.0 2007 1812 115 Comp. Ex. x13 Mn 0.5 2004 1820 117 Comp. Ex. x14 2.0 2005 1822 110 Comp. Ex. x15 B 0.5 2003 1824 115 Comp. Ex. x16 2.0 2002 1825 117 Comp. Ex. x17 W 0.5 2008 1822 119 Comp. Ex. x18 2.0 2008 1820 116 Comp. Ex. x19 Nb 0.5 2009 1821 122 Comp. Ex. x20 2.0 2010 1822 100 Comp. Ex. x21 Mo 0.5 2007 1824 112 Comp. Ex. x22 2.0 2009 1822 110 Comp. Ex. x23 Ta 2.5 1990 1720 118 Comp. Ex. x24 Al 1992 1721 112 Comp. Ex. x25 Zr 1991 1710 117 Comp. Ex. x26 Mg 1993 1712 120 Comp. Ex. x27 In 1992 1719 118 Comp. Ex. x28 Sn 1990 1711 115 Comp. Ex. x29 Mn 1992 1712 105 Comp. Ex. x30 B 1992 1710 110 Comp. Ex. x31 W 1990 1720 117 Comp. Ex. x32 Nb 1991 1721 118 Comp. Ex. x33 Mo 1990 1710 120 Comp. Ex. x34 Ta 0.5 60 · 55 1800 1621 115 Comp. Ex. x35 Al 1801 1618 110 Comp. Ex. x36 Zr 1802 1611 112 Comp. Ex. x37 Mg 1804 1610 125 Comp. Ex. x38 In 1805 1612 115 Comp. Ex. x39 Sn 1802 1600 105 Comp. Ex. x40 Mn 1807 1609 120 Comp. Ex. x41 B 1803 1608 120 Comp. Ex. x42 W 1804 1610 100 Comp. Ex. x43 Nb 1802 1620 120 Comp. Ex. x44 Mo 1801 1618 110 Comp. Ex. x45 Ta 0.5 Absent 25 · 20 2000 1810 120 Comp. Ex. x46 Al 2001 1809 120 Comp. Ex. x47 Zr 2000 1802 100 Comp. Ex. x48 Mg 2000 1809 118 Comp. Ex. x49 In 2002 1810 117 Comp. Ex. x50 Sn 2000 1812 113 Comp. Ex. x51 Mn 1999 1809 120 Comp. Ex. x52 B 1998 1800 120 Comp. Ex. x53 W 2000 1803 115 Comp. Ex. x54 Nb 2001 1801 115 Comp. Ex. x55 Mo 2002 1812 118 Comp. Ex. x56 Not — Present 25 · 55 1990 1700 115 Comp. Ex. x57 Added Absent Mixed Gas of 2010 1820 140 Nitrogen:Hydrogen = 95:5 (molar ratio) treated at 400° C. for 6 hours Comp. Ex. x58 Not Carried Out 2009 1819 142

The results of Table 24 made clear that when Li_(1.03)NiO₂ was used, though the domain having the NaCl-type crystal structure was produced, the discharge capacity was small. With an excessive presence of Li as well, when Z is greater than 0.5 in Li_(x)Ni_(1-y-z)Co_(y)Me_(x)O₂, a homogeneous solid solution could not be obtained.

INDUSTRIAL APPLICABILITY

The present invention is useful in a lithium ion secondary battery including a lithium-nickel composite oxide composed mainly of nickel as the positive electrode active material. Based on the present invention, safety upon internal short-circuit can be further improved without hindering high-rate performance at low temperature.

Form of a lithium ion secondary battery of the present invention is not particularly limited, and may be any of for example coin-type, button-type, sheet-type, cylindrical type, flat-type, and prismatic-type. Also, form of an electrode assembly including a positive electrode, a negative electrode, and a separator may be wound-type or stack-type. The size of the battery may be a small size for a small mobile devices, or may be a large size for electric vehicles. Thus, a lithium ion secondary battery of the present invention may be used as a power source for, for example, personal data assistants, mobile electronic devices, household small electric power storage devices, motorcycles, Electric Vehicles, and Hybrid Electric Vehicles. However, application is not particularly limited. 

1. A lithium ion secondary battery comprising a positive electrode capable of charging and discharging, a negative electrode capable of charging and discharging, and a non-aqueous electrolyte; said positive electrode including active material particles; said active material particles including at least a first lithium-nickel composite oxide forming a core portion thereof; said first lithium-nickel composite oxide being represented by Li_(x)Ni_(1-y-z)Co_(y)Me_(x)O₂ where 0.85≦x≦1.25, 0<y≦0.5, 0≦z≦0.5, 0<y+z≦0.75, and element Me is at least one selected from the group consisting of Al, Mn, Ti, Mg, and Ca; a surface layer portion of said active material particles including: (i) at least one selected from the group consisting of a nickel oxide having a NaCl crystal structure and a second lithium-nickel composite oxide including a domain having the NaCl crystal structure; and (ii) element M not incorporated in the crystal structure of said first lithium-nickel composite oxide, said element M being at least one selected from the group consisting of Al, Mn, Mg, B, Zr, W, Nb, Ta, In, Mo, and Sn.
 2. The lithium ion secondary battery in accordance with claim 1, wherein said nickel oxide having the NaCl crystal structure is at least one selected from the group consisting of NiO and cation-deficient Ni_(1-δ)O, and said domain having the NaCl crystal structure has a structure in which Li in Li site in said first lithium-nickel composite oxide is replaced with Ni, Co, or Me.
 3. The lithium ion secondary battery in accordance with claim 1, wherein element M is distributed more at the outer side of said surface layer portion compared with the inner side thereof, and said nickel oxide is distributed more at the inner side of said surface layer portion compared with the outer side.
 4. The lithium ion secondary battery in accordance with claim 1, wherein 0<z≦0.5, and the concentration of element Me is high in the proximity of said surface layer portion compared with the inner portion of said active material particles.
 5. The lithium ion secondary battery in accordance with claim 1, wherein the amount of element M is 2 mol % or less relative to said first lithium-nickel composite oxide.
 6. A method for producing a lithium ion secondary battery, the method comprising the steps of: obtaining a positive electrode capable of charging and discharging; obtaining a negative electrode capable of charging and discharging; and assembling a battery including said positive electrode, said negative electrode, and a non-aqueous electrolyte: said step of obtaining said positive electrode including the steps of: (i) allowing a first lithium-nickel composite oxide represented by Li_(x)Ni_(1-y-z)Co_(y)Me_(x)O₂ where 0.85≦x≦1.25, 0<y≦0.5, 0≦z≦0.5, 0<y+z≦0.75, and element Me is at least one selected from the group consisting of Al, Mn, Ti, Mg, and Ca, to carry element M of at least one selected from the group consisting of Al, Mn, Mg, B, Zr, W, Nb, Ta, In, Mo, and Sn; (ii) producing NiOOH on a surface of said first lithium-nickel composite oxide by moisture in the atmosphere by allowing said first lithium-nickel composite oxide carrying element M to stand under an environment with a temperature of 60° C. or less and a humidity of 20% or more; (iii) preliminary baking said first lithium-nickel composite oxide with NiOOH produced on the surface thereof in a dry air atmosphere, and then carrying out a main baking in an oxygen atmosphere, thereby converting said NiOOH into at least one selected from the group consisting of NiO having a NaCl crystal structure, cation-deficient Ni_(1-δ)O having the NaCl-type crystal structure, and a second lithium-nickel composite oxide including a domain having the NaCl crystal structure, to obtain active material particles; and (iv) forming a positive electrode including said active material particles. 